fix: change phone constraint to per user (#1713)

## What kind of change does this PR introduce?

Currently, the phone constraint only allows for one phone number across
all users. Changes to make phone numbers unique per user.

Also renames the constraint on phone factors to reflect that it applies
to all factors rather than verified factors.

migrations/20240806073726_drop_uniqueness_constraint_on_phone.up.sql

@@ -0,0 +1,12 @@
+alter table {{ index .Options "Namespace" }}.mfa_factors drop constraint if exists mfa_factors_phone_key;
+do $$
+begin
+    if exists (
+         select 1
+         from pg_indexes
+         where indexname = 'unique_verified_phone_factor'
+         and schemaname = '{{ index .Options "Namespace" }}'
+    ) then
+        execute 'alter index {{ index .Options "Namespace" }}.unique_verified_phone_factor rename to unique_phone_factor_per_user';
+    end if;
+end $$;