ua: reduce usage of `tenant 2` as an application tenant from tests

[shubhamdhama]

This issue is a sub-issue of #151327

There are around 31 usages of roachpb.MustMakeTenantID(2) in tests used for application tenant. We should be replacing them with tenant id 3. This would align with real world scenario where tenant with id 2 doesn't exist, which is enforced in demo cluster and normal operations. And if a cluster goes through UA migration, tenant 2 would be a system tenant.

Jira issue: CRDB-46349