feat: add configurable cooldown to claim usernames (#6422)

Add a new option that allows instances to set a cooldown period to claim
old usernames. In the context of public instances this can be used to
prevent old usernames to be claimed after they are free and allow
graceful migration (by making use of the redirect feature) to a new
username. The granularity of this cooldown is a day. By default this
feature is disabled and thus no cooldown period.

The `CreatedUnix` column is added the `user_redirect` table, for
existing redirects the timestamp is simply zero as we simply do not know
when they were created and are likely already over the cooldown period
if the instance configures one.

Users can always reclaim their 'old' user name again within the cooldown
period. Users can also always reclaim 'old' names of organization they
currently own within the cooldown period.

Creating and renaming users as an admin user are not affected by the
cooldown period for moderation and user support reasons.

To avoid abuse of the cooldown feature, such that a user holds a lot of
usernames, a new option is added `MAX_USER_REDIRECTS` which sets a limit
to the amount of user redirects a user may have, by default this is
disabled. If a cooldown period is set then the default is 5. This
feature operates independently of the cooldown period feature.

Added integration and unit testing.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/6422
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Reviewed-by: 0ko <0ko@noreply.codeberg.org>
Reviewed-by: Otto <otto@codeberg.org>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

options/locale/locale_en-US.ini

@@ -630,6 +630,7 @@ lang_select_error = Select a language from the list.
 
 username_been_taken = The username is already taken.
 username_change_not_local_user = Non-local users are not allowed to change their username.
+username_claiming_cooldown = The username cannot be claimed, because its cooldown period is not yet over. It can be claimed on %[1]s.
 repo_name_been_taken = The repository name is already used.
 repository_force_private = Force Private is enabled: private repositories cannot be made public.
 repository_files_already_exist = Files already exist for this repository. Contact the system administrator.
@@ -765,6 +766,8 @@ update_profile_success = Your profile has been updated.
 change_username = Your username has been changed.
 change_username_prompt = Note: Changing your username also changes your account URL.
 change_username_redirect_prompt = The old username will redirect until someone claims it.
+change_username_redirect_prompt.with_cooldown.one = The old username will be available to everyone after a cooldown period of %[1]d day, you can still reclaim the old username during the cooldown period.
+change_username_redirect_prompt.with_cooldown.few = The old username will be available to everyone after a cooldown period of %[1]d days, you can still reclaim the old username during the cooldown period.
 continue = Continue
 cancel = Cancel
 language = Language
@@ -2883,6 +2886,8 @@ settings.update_settings = Update settings
 settings.update_setting_success = Organization settings have been updated.
 settings.change_orgname_prompt = Note: Changing the organization name will also change your organization's URL and free the old name.
 settings.change_orgname_redirect_prompt = The old name will redirect until it is claimed.
+settings.change_orgname_redirect_prompt.with_cooldown.one = The old username will be available to everyone after a cooldown period of %[1]d day, you can still reclaim the old username during the cooldown period.
+settings.change_orgname_redirect_prompt.with_cooldown.few = The old username will be available to everyone after a cooldown period of %[1]d days, you can still reclaim the old username during the cooldown period.
 settings.update_avatar_success = The organization's avatar has been updated.
 settings.delete = Delete organization
 settings.delete_account = Delete this organization