Add primary key to repo_topic table

[mihkelvain]

• Git version: 1.9.5
• Operating system: CentOS 7
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No
  • Not relevant
• Log gist:

Description

In MySQL group replication, it is mandatory to that every table has primary key. Gitea schema has repo_topic table that does not have primary key. Please consider adding pk also to that table.
https://dev.mysql.com/doc/refman/8.0/en/group-replication-requirements.html

Currently gitea runs fine in group replicated mysql instance, but for obvious reasons I can't alter repo topics.

[lafriks]

UNIQUE index for that table could be easily replaced by composite PK

[zeripath]

I suspect that this would require #12407 to recreate the tables with the primary key. SQLite certainly requires the tables to be recreated. Others would cause us to have to do constraint checking - recreating would certainly be simpler.