Display original author and URL information when showing migrated issues/comments...

Display original author and URL information when showing migrated issues/comments (#7352)

* Store original author info for migrated issues and comments

Keep original author name for displaying in Gitea interface and also
store original author user ID for potential future use in linking
accounts from old location.

* Add original_url for repo

Store the original URL for a migrated repo

Clean up migrations/tests

* fix migration

* fix golangci-lint

* make 'make revive' happy also

* Modify templates to use OriginalAuthor if set

Use the original author name in templates if it is set rather than the
user who migrated/currently owns the issues

* formatting fixes

* make generate-swagger

* Use default avatar for imported comments

* Remove no longer used IgnoreIssueAuthor option

* Add OriginalAuthorID to swagger also