[META] Add CODEOWNERS files

- As per https://codeberg.org/forgejo/discussions/issues/53#issuecomment-1070207
- Using the `CODEOWNERS` feature it should speed up the development
process for contributors as for the most common PRs the right reviewers
will be added by Forgejo automatically. They can be added very
precisely according to the changed files of the PR.
- This feature is implemented in v1.21, which means it's not available
on Codeberg.

(cherry picked from commit 1511ef1c803f31fcf2887611982a114465f3be60)
(cherry picked from commit 99999e3a034b719dcefc63951538d917dfd9e496)
(cherry picked from commit 0b0dd6f7a95ce718c8ff73e8e6fe1b660a4e3277)
(cherry picked from commit d42940034f7fe1f1f706e4fff8f9b5c8465003fc)
(cherry picked from commit 5be6e7d2542e6915d1df3d9f29a8504f851b8f52)
(cherry picked from commit d12d6e8633a9f88c1283a3613f8dc1ffff1acacb)
(cherry picked from commit d3b3e691bfad6713b92ee636ddba953b897bfbbd)
(cherry picked from commit 2a13f95551b323a52ea20823760b5ecdc629233a)

CODEOWNERS

@@ -0,0 +1,32 @@
+# This file describes the expected reviewers for a PR based on the changed
+# files. Unlike what the name of the file suggests they don't own the code, but
+# merely have a good understanding of that area of the codebase and therefore
+# are usually suited as a reviewer.
+
+
+# Please mind the alphabetic order of reviewers.
+
+# Files related to the CI of the Forgejo project.
+.forgejo/.* @dachary @earl-warren
+
+# Files related to frontend development.
+
+# Javascript and CSS code.
+web_src/.* @caesar @crystal @gusted
+
+# HTML templates used by the backend.
+templates/.* @caesar @crystal @gusted
+
+# Files related to Go development.
+
+# The modules usually don't require much knowledge about Forgejo and could
+# be reviewed by Go developers.
+modules/.* @dachary @earl-warren @gusted
+
+# Models has code related to SQL queries, general database knowledge and XORM.
+models/.* @dachary @earl-warren @gusted
+
+# The routers directory contains the most amount code that requires a good grasp
+# of how Forgejo comes together. It's tedious to write good integration testing
+# for code that lives in here.
+routers/.* @dachary @earl-warren @gusted