Forms (internal): Add placeholder text for MemberID fields

[eastofesten]

Motivation

On the Members Dashboard, we have placeholder text to let users know to search by email:

The lack of this text on a create/edit pub form adds confusion for users who attempt to search by name, or who then try to add a new user (not realizing where the email is supposed to be entered:

Requirements

• Add placeholder text to MemberId field to match the Members Dashboard

Acceptance Criteria