Add command to bulk set must-change-password (#22823)

As part of administration sometimes it is appropriate to forcibly tell
users to update their passwords.

This PR creates a new command `gitea admin user must-change-password`
which will set the `MustChangePassword` flag on the provided users.

Signed-off-by: Andrew Thornton <art27@cantab.net>

docs/content/doc/usage/command-line.en-us.md

@@ -99,6 +99,13 @@ Admin operations:
         - `--password value`, `-p value`: New password. Required.
       - Examples:
         - `gitea admin user change-password --username myname --password asecurepassword`
+    - `must-change-password`:
+      - Args:
+        - `[username...]`: Users that must change their passwords
+      - Options:
+        - `--all`, `-A`: Force a password change for all users
+        - `--exclude username`, `-e username`: Exclude the given user. Can be set multiple times.
+        - `--unset`: Revoke forced password change for the given users
   - `regenerate`
     - Options:
       - `hooks`: Regenerate Git Hooks for all repositories