fix: Make bloat portable

• Adjusts the saturation metrics for postgres bloat to be more portable across observability systems
• The job label differs between different monitoring solutions, this is technically not needed anyways.
• To make these rules more friendly the operator should use the appropriate selectors instead.

One can view that nothing actually changes for our metrics for .com with this change by going to this absurdly long Thanos URL

The changing queries that exist are presented on their accompanying alerts dashboard:

• btree_bloat: https://dashboards.gitlab.net/d/alerts-sat_pg_btree_bloat/alerts3a-pg-btree-bloat3a-saturation-detail
• table_bloat: https://dashboards.gitlab.net/d/alerts-sat_pg_table_bloat/alerts3a-pg-table-bloat3a-saturation-detail

I expect no change to the results of these queries after this change is merged.

Addresses: https://gitlab.com/gitlab-com/gl-infra/gitlab-dedicated/team/-/issues/2902