Add solved tag/label to forums consistently

Fixed for the bug tracker forums which are IMHO most important. Other forums need individual attention but I think not worth keeping an issue on JIRA open for that.

Barely saw any solved prefixes in forums...

https://forum.armbian.com/topic/12854-moderation-better-using-report-this-content-flagging-for-mentoring-new-mods/?do=findComment&comment=104794

will leave open for a day or 2 to await feedback

I made label system open. I manually added solved prefix to most forums.

it’s easy for me to clean up bad labels from admin panel