Add support for incoming emails (#22056)

closes #13585
fixes #9067
fixes #2386
ref #6226
ref #6219
fixes #745

This PR adds support to process incoming emails to perform actions.
Currently I added handling of replies and unsubscribing from
issues/pulls. In contrast to #13585 the IMAP IDLE command is used
instead of polling which results (in my opinion 😉) in cleaner code.

Procedure:
- When sending an issue/pull reply email, a token is generated which is
present in the Reply-To and References header.
- IMAP IDLE waits until a new email arrives
- The token tells which action should be performed

A possible signature and/or reply gets stripped from the content.

I added a new service to the drone pipeline to test the receiving of
incoming mails. If we keep this in, we may test our outgoing emails too
in future.

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

3 files changed, 3 insertions, 3 deletions

diff --git a/docs/content/doc/features/comparison.en-us.md b/docs/content/doc/features/comparison.en-us.md
index 9baa6d5123..87b2f43de7 100644
--- a/docs/content/doc/features/comparison.en-us.md
+++ b/docs/content/doc/features/comparison.en-us.md
@@ -106,7 +106,7 @@ _Symbols used in table:_
 | Issue search                  | ✓                                                   | ✘    | ✓         | ✓         | ✓         | ✓         | ✘            |
 | Global issue search           | [/](https://github.com/go-gitea/gitea/issues/2434)  | ✘    | ✓         | ✓         | ✓         | ✓         | ✘            |
 | Issue dependency              | ✓                                                   | ✘    | ✘         | ✘         | ✘         | ✘         | ✘            |
-| Create issue via email        | [✘](https://github.com/go-gitea/gitea/issues/6226)  | ✘    | ✘         | ✘         | ✓         | ✓         | ✘            |
+| Create issue via email        | [✘](https://github.com/go-gitea/gitea/issues/6226)  | ✘    | ✘         | ✓         | ✓         | ✓         | ✘            |
 | Service Desk                  | [✘](https://github.com/go-gitea/gitea/issues/6219)  | ✘    | ✘         | ✓         | ✓         | ✘         | ✘            |
 
 ## Pull/Merge requests
diff --git a/docs/content/doc/features/comparison.zh-cn.md b/docs/content/doc/features/comparison.zh-cn.md
index aaf8eb4abc..c5bec58cb8 100644
--- a/docs/content/doc/features/comparison.zh-cn.md
+++ b/docs/content/doc/features/comparison.zh-cn.md
@@ -92,7 +92,7 @@ _表格中的符号含义:_
 | 工单搜索            | ✓                                                  | ✘                                             | ✓         | ✓                                                                       | ✓         | ✓              | ✘            |
 | 工单全局搜索        | [✘](https://github.com/go-gitea/gitea/issues/2434) | ✘                                             | ✓         | ✓                                                                       | ✓         | ✓              | ✘            |
 | 工单依赖关系        | ✓                                                  | ✘                                             | ✘         | ✘                                                                       | ✘         | ✘              | ✘            |
-| 通过 Email 创建工单 | [✘](https://github.com/go-gitea/gitea/issues/6226) | [✘](https://github.com/gogs/gogs/issues/2602) | ✘         | ✘                                                                       | ✓         | ✓              | ✘            |
+| 通过 Email 创建工单 | [✘](https://github.com/go-gitea/gitea/issues/6226) | [✘](https://github.com/gogs/gogs/issues/2602) | ✘         | ✓                                                                       | ✓         | ✓              | ✘            |
 | 服务台              | [✘](https://github.com/go-gitea/gitea/issues/6219) | ✘                                             | ✘         | [✓](https://gitlab.com/groups/gitlab-org/-/epics/3103)                  | ✓         | ✘              | ✘            |
 
 #### Pull/Merge requests
diff --git a/docs/content/doc/features/comparison.zh-tw.md b/docs/content/doc/features/comparison.zh-tw.md
index 015955f0a8..4da9c74ec8 100644
--- a/docs/content/doc/features/comparison.zh-tw.md
+++ b/docs/content/doc/features/comparison.zh-tw.md
@@ -93,7 +93,7 @@ menu:
 | 問題搜尋             | ✓                                                  | ✘                                             | ✓         | ✓                                                                       | ✓         | ✓         | ✘            |
 | 全域問題搜尋         | [✘](https://github.com/go-gitea/gitea/issues/2434) | ✘                                             | ✓         | ✓                                                                       | ✓         | ✓         | ✘            |
 | 問題相依             | ✓                                                  | ✘                                             | ✘         | ✘                                                                       | ✘         | ✘         | ✘            |
-| 從電子郵件建立問題   | [✘](https://github.com/go-gitea/gitea/issues/6226) | [✘](https://github.com/gogs/gogs/issues/2602) | ✘         | ✘                                                                       | ✓         | ✓         | ✘            |
+| 從電子郵件建立問題   | [✘](https://github.com/go-gitea/gitea/issues/6226) | [✘](https://github.com/gogs/gogs/issues/2602) | ✘         | ✓                                                                       | ✓         | ✓         | ✘            |
 | 服務台               | [✘](https://github.com/go-gitea/gitea/issues/6219) | ✘                                             | ✘         | [✓](https://gitlab.com/groups/gitlab-org/-/epics/3103)                  | ✓         | ✘         | ✘            |
 
 ## 拉取/合併請求