Fix #28157
Backport #28691 

This PR fix the possible bugs about actions schedule.

- Move `UpdateRepositoryUnit` and `SetRepoDefaultBranch` from models to
service layer
- Remove schedules plan from database and cancel waiting & running
schedules tasks in this repository when actions unit has been disabled
or global disabled.
- Remove schedules plan from database and cancel waiting & running
schedules tasks in this repository when default branch changed.

Currently 'userxx' and 'orgxx' are both used as username in test files
when the user type is org, which is confusing. This PR replaces all
'userxx' with 'orgxx' when the user type is org(`user.type==1`).
Some non-trivial changes
1. Rename `user3` dir to `org3` in `tests/git-repositories-meta` 
2. Change `end` in `issue reference` because 'org3' is one char shorter
than 'user3'

![ksnip_20230913-112819](https://github.com/go-gitea/gitea/assets/70063547/442988c5-4cf4-49b8-aa01-4dd6bf0ca954)
3. Change the search result number of `user/repo2` because
`user3/repo21` can't be searched now

![ksnip_20230913-112931](https://github.com/go-gitea/gitea/assets/70063547/d9ebeba4-479f-4110-9a85-825efbc981fd)
4. Change the first org name getting from API because the result is
ordered by alphabet asc and now `org 17` is before `org25`
![JW8U7NIO(J$H
_YCRB36H)T](https://github.com/go-gitea/gitea/assets/70063547/f55a685c-cf24-40e5-a87f-3a2327319548)
![)KFD411O4I8RB5ZOH7E0
Z3](https://github.com/go-gitea/gitea/assets/70063547/a0dc3299-249c-46f6-91cb-d15d4ee88dd5)

Other modifications are just find all and replace all.
Unit tests with SQLite are all passed.

---------

Co-authored-by: caicandong <1290147055@qq.com>

Repository creation depends on many models, so moving it to service
layer is better.

Follow #25229

Copy from
https://github.com/go-gitea/gitea/pull/26290#issuecomment-1663135186

The bug is that we cannot get changed files for the
`pull_request_target` event. This event runs in the context of the base
branch, so we won't get any changes if we call
`GetFilesChangedSinceCommit` with `PullRequest.Base.Ref`.

Before: the concept "Content string" is used everywhere. It has some
problems:

1. Sometimes it means "base64 encoded content", sometimes it means "raw
binary content"
2. It doesn't work with large files, eg: uploading a 1G LFS file would
make Gitea process OOM

This PR does the refactoring: use "ContentReader" / "ContentBase64"
instead of "Content"

This PR is not breaking because the key in API JSON is still "content":
`` ContentBase64 string `json:"content"` ``

Follow #25229

At present, when the trigger event is `pull_request_target`, the `ref`
and `sha` of `ActionRun` are set according to the base branch of the
pull request. This makes it impossible for us to find the head branch of
the `ActionRun` directly. In this PR, the `ref` and `sha` will always be
set to the head branch and they will be changed to the base branch when
generating the task context.

Fix #25088

This PR adds the support for
[`pull_request_target`](https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#pull_request_target)
workflow trigger. `pull_request_target` is similar to `pull_request`,
but the workflow triggered by the `pull_request_target` event runs in
the context of the base branch of the pull request rather than the head
branch. Since the workflow from the base is considered trusted, it can
access the secrets and doesn't need approvals to run.