feat(datastore): add remaining indexes on layers for alternative namespace usage query

Continues and completes the work started in !1163 (merged) by creating the index on the remaining 62 partitions and parent table.

The first post-deployment migration (introduced in !1163 (merged)), containing the indexes for partitions 0 and 1, was successfully applied in production (gitlab-com/gl-infra/production#8165 (closed)). From that, we learned that it took 30s to create the two indexes, so an average of 15s per index.

The new 62 partition indexes were split into 4 migrations. The idea is to keep each migration under 5 minutes of execution. We then have an additional migration just for the parent table.

Related to #853 (closed)