Investigate if we can drop index_users_require_two_factor_authentication_from_group_false

As part of reducing lightweight lock contention, investigate if it's possible to drop the index index_users_require_two_factor_authentication_from_group_false from the namespaces table.

• Find out when and why the index was added
• Decide if the index can be dropped
• Drop the index if possible
• If the index cannot be dropped, document the reason in a comment on this issue and close.

In case we are not able to drop this index, we should at least replace it, together with index_users_require_two_factor_authentication_from_group, with single index without WHERE:

"index_users_on_require_two_factor_authentication_from_group" btree (require_two_factor_authentication_from_group) WHERE require_two_factor_authentication_from_group = true

"index_users_require_two_factor_authentication_from_group_false" btree (require_two_factor_authentication_from_group) WHERE require_two_factor_authentication_from_group = false

Index usage on Thanos.