Support .git-blame-ignore-revs file (#26395)

Closes #26329

This PR adds the ability to ignore revisions specified in the
`.git-blame-ignore-revs` file in the root of the repository.


![grafik](https://github.com/go-gitea/gitea/assets/1666336/9e91be0c-6e9c-431c-bbe9-5f80154251c8)

The banner is displayed in this case. I intentionally did not add a UI
way to bypass the ignore file (same behaviour as Github) but you can add
`?bypass-blame-ignore=true` to the url manually.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

docs/content/usage/blame.en-us.md

@@ -0,0 +1,38 @@
+---
+date: "2023-08-14T00:00:00+00:00"
+title: "Blame File View"
+slug: "blame"
+sidebar_position: 13
+toc: false
+draft: false
+aliases:
+  - /en-us/blame
+menu:
+  sidebar:
+    parent: "usage"
+    name: "Blame"
+    sidebar_position: 13
+    identifier: "blame"
+---
+
+# Blame File View
+
+Gitea supports viewing the line-by-line revision history for a file also known as blame view.
+You can also use [`git blame`](https://git-scm.com/docs/git-blame) on the command line to view the revision history of lines within a file.
+
+1. Navigate to and open the file whose line history you want to view.
+1. Click the `Blame` button in the file header bar.
+1. The new view shows the line-by-line revision history for a file with author and commit information on the left side.
+1. To navigate to an older commit, click the ![versions](/octicon-versions.svg) icon.
+
+## Ignore commits in the blame view
+
+All revisions specified in the `.git-blame-ignore-revs` file are hidden from the blame view.
+This is especially useful to hide reformatting changes and keep the benefits of `git blame`.
+Lines that were changed or added by an ignored commit will be blamed on the previous commit that changed that line or nearby lines.
+The `.git-blame-ignore-revs` file must be located in the root directory of the repository.
+For more information like the file format, see [the `git blame --ignore-revs-file` documentation](https://git-scm.com/docs/git-blame#Documentation/git-blame.txt---ignore-revs-fileltfilegt).
+
+### Bypassing `.git-blame-ignore-revs` in the blame view
+
+If the blame view for a file shows a message about ignored revisions, you can see the normal blame view by appending the url parameter `?bypass-blame-ignore=true`.

docs/static/octicon-versions.svg

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