Generate custom abilities documentation

What does this MR do and why?

It generates available custom abilities documentation by running bundle exec rake gitlab:custom_roles:compile_docs

Follow-up issue: Add verification that custom abilities doc is u... (#437662 - closed)

Closes #434352 (closed)

doc/development/permissions/custom_roles.md

@@ -186,6 +186,7 @@ To add a new ability to a custom role:
 - Add a new column to `member_roles` table, either manually or by running `custom_roles:code`  generator, eg. by running `rails generate gitlab:custom_roles:code --ability new_ability_name`. The ability parameter is case sensitive and has to exactly match the permission name from the YAML file.
 - Add the ability to the respective Policy for example in [this change in merge request 114734](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/114734/diffs#diff-content-edcbe28bdecbd848d4d9efdc5b5e9bddd2a7299e).
 - Update the specs. Don't forget to add a spec to `ee/spec/requests/custom_roles` - the spec template file was generated if you used the code generator
+- Compile the documentation by running `bundle exec rake gitlab:custom_roles:compile_docs`
 
 Examples of merge requests adding new abilities to custom roles: