This PR fixes a mistake from the previous PR
#18342. Merged configuration results
in the customization being an array not an object.

This PR also moves `displayApps` from being an array to being an object,
like the terraform provider has.

Adds database migrations required for the Tasks feature.

There's a slight difference between the migrations in this PR and the
RFC: this PR adds `NOT NULL` constraints to the `has_ai_task` columns.
It was an oversight on my part when I wrote the RFC - I assumed the
`DEFAULT FALSE` value would make the columns implicitly NOT NULL, but
that's not the case with Postgres. We have no use for the NULL value.

The `DEFAULT FALSE` statement ensures that the migration will pass even
when there are existing rows in the template version and workspace
builds tables, so there's no danger in adding the `NOT NULL`
constraints.