The automation plugin has 4 custom field types that are array typed. However, array typed custom fields are deprecated and should be migrated to JSON type.
This commit does a couple of things:
1. Migrate all four custom fields to JSON
2. Fix a couple of small bugs that have been discovered while migrating the custom fields to JSON (see the comments on this commit's PR for details https://github.com/discourse/discourse/pull/26939)
When the admin creates a new custom field they can specify if that field should be searchable or not.
That setting is taken into consideration for quick search results.
User.publish_notifications_state is called every time a notification is
created, this can become a very critical code path.
On some heavy notification related sites this can be a major CPU user on PG
This index makes it much cheaper to publish notification state, cause a
simple index lookup does the trick.
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
