[Hotfix] Add BaseFileNode index for target/provider/type

[mfraezz]

Purpose

Avoid costly BitmapHeap Scan when doing things like OsfStorageFolder.objects.filter(target=node), etc.

Changes

• Alter index_together

QA Notes

See if files load any faster? No direct UI changes, may not affect the generic file page queries (especially not until the table is vacuumed, which happens automatically over long periods of time). Added specifically to further optimize #8849

Side Effects

None expected, other than what's listed below

Deployment Notes

Because this is decently-sized index on one of our largest tables, this MUST NOT be deployed without downtime. Indices require exclusive table locks while being created*, therefore this requires maintenance downtime.

* Except concurrently, which is technically possible but not supported by Django. Doing so would require the migration operation to be something like:

migrations.SeparateDatabaseAndState(
    state_operations=[
        migrations.AlterIndexTogether(
            model_name='basefilenode',
            index_together=set([('target_content_type', 'target_object_id'), ('target_content_type', 'target_object_id', 'provider', 'type')]),
        ),
    ],
    database_operations=[
        migrations.RunSQL([
            'CREATE INDEX CONCURRENTLY "osf_basefilenode_toid_tcid_prv_type_deadbeef_idx" ON "osf_basefilenode" ("target_object_id", "target_content_type_id", "provider", "type");',
        ], [
            'DROP INDEX IF EXISTS "osf_basefilenode_toid_tcid_prv_type_deadbeef_idx", RESTRICT;'
        ])
    ]
)

However, due to caveats, it's possible that index would not be successfully created, leading to increased overhead and none of the benefits, and possible deadlock during the failed creation process.

Ticket

None known