Added membersContainsFilters labs flag

refs https://github.com/TryGhost/Team/issues/1408

- flag for gating access to "Name" and "Email" members filters in Admin

core/shared/labs.js

@@ -37,6 +37,7 @@ const ALPHA_FEATURES = [
     'membersTableStatus',
     'membersLastSeenFilter',
     'membersTimeFilters',
+    'membersContainsFilters',
     'selectablePortalLinks'
 ];