dbpurge: purge expired api keys #19889

Relates to:

• perf(coderd/database): optimize GetAPIKeysLastUsedAfter #19725
• fix: expire token for prebuilds user when regenerating session token #19667
• fix: don't create new api keys each time we do workspace polling jetbrains-coder#568

#19725 added an index to reduce the impact of large numbers of API keys on the UI.

#19667 adds logic to dbpurge to expire API keys belonging to the prebuilds user

jetbrains-coder#568 fixed an issue with the JetBrains plugin that caused large numbers of API keys to be created.

As a separate follow-up to this, add logic to dbpurge to delete expired API keys created by the JetBrains plugin to reduce the size of the database.