Add the ability to pin Issues (#24406)

This adds the ability to pin important Issues and Pull Requests. You can
also move pinned Issues around to change their Position. Resolves #2175.

## Screenshots

![grafik](https://user-images.githubusercontent.com/15185051/235123207-0aa39869-bb48-45c3-abe2-ba1e836046ec.png)

![grafik](https://user-images.githubusercontent.com/15185051/235123297-152a16ea-a857-451d-9a42-61f2cd54dd75.png)

![grafik](https://user-images.githubusercontent.com/15185051/235640782-cbfe25ec-6254-479a-a3de-133e585d7a2d.png)

The Design was mostly copied from the Projects Board.

## Implementation
This uses a new `pin_order` Column in the `issue` table. If the value is
set to 0, the Issue is not pinned. If it's set to a bigger value, the
value is the Position. 1 means it's the first pinned Issue, 2 means it's
the second one etc. This is dived into Issues and Pull requests for each
Repo.

## TODO
- [x] You can currently pin as many Issues as you want. Maybe we should
add a Limit, which is configurable. GitHub uses 3, but I prefer 6, as
this is better for bigger Projects, but I'm open for suggestions.
- [x] Pin and Unpin events need to be added to the Issue history.
- [x] Tests
- [x] Migration

**The feature itself is currently fully working, so tester who may find
weird edge cases are very welcome!**

---------

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Giteabot <teabot@gitea.io>

3 files changed, 10 insertions, 0 deletions

diff --git a/modules/structs/issue.go b/modules/structs/issue.go
index 04e169df84..a9fb6c6e79 100644
--- a/modules/structs/issue.go
+++ b/modules/structs/issue.go
@@ -75,6 +75,8 @@ type Issue struct {
 
 	PullRequest *PullRequestMeta `json:"pull_request"`
 	Repo        *RepositoryMeta  `json:"repository"`
+
+	PinOrder int `json:"pin_order"`
 }
 
 // CreateIssueOption options to create one issue
diff --git a/modules/structs/pull.go b/modules/structs/pull.go
index a4a6f60b05..05a8d59633 100644
--- a/modules/structs/pull.go
+++ b/modules/structs/pull.go
@@ -49,6 +49,8 @@ type PullRequest struct {
 	Updated *time.Time `json:"updated_at"`
 	// swagger:strfmt date-time
 	Closed *time.Time `json:"closed_at"`
+
+	PinOrder int `json:"pin_order"`
 }
 
 // PRBranchInfo information about a branch
diff --git a/modules/structs/repo.go b/modules/structs/repo.go
index 01239188c2..fc4ed03de5 100644
--- a/modules/structs/repo.go
+++ b/modules/structs/repo.go
@@ -374,3 +374,9 @@ type RepoTransfer struct {
 	Recipient *User   `json:"recipient"`
 	Teams     []*Team `json:"teams"`
 }
+
+// NewIssuePinsAllowed represents an API response that says if new Issue Pins are allowed
+type NewIssuePinsAllowed struct {
+	Issues       bool `json:"issues"`
+	PullRequests bool `json:"pull_requests"`
+}