The `commit_id` property name is the same as equivalent functionality in
GitHub. If the action was not caused by a commit, an empty string is
used.
This can for example be used to automatically add a Resolved label to an
issue fixed by a commit, or clear it when the issue is reopened.
Previously, there was an `import services/webhooks` inside
`modules/notification/webhook`.
This import was removed (after fighting against many import cycles).
Additionally, `modules/notification/webhook` was moved to
`modules/webhook`,
and a few structs/constants were extracted from `models/webhooks` to
`modules/webhook`.
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
