Remove member email validation

In OSDU, a user id could be anything and may not be in email format. The current code contains the latency logic in the original SLB implementation, but it is not applicable for OSDU.

To resolve this issue, we have to remove the member email validation logic in the POST groups/{group_email}/members API and allows the service to add any user id into a group.

As a note, the group id is still in email format and will be something like group_name@{partitionid}.{DOMAIN}. Since the entitlements v2 service allows to add group hierarchy (adding a group into another group) and it is the same POST API as adding user into a group. The service will still use the {DOMAIN} suffix to determine whether the given member is a group or user.