Migrates validation and mutation of RT GR, and GRB

[KevinJoiner]

This commit migrates validation and mutation for RoleTemplates
GlobalRoles and GlobalRoleBindings which were previously performed
via Norman.

Problem

Some validation for RoleTemplates, GlobalRoles, and GlobalRoleBindings only lived in Norman.

Solution

All validation will be performed by the webhook.

Testing

This commit contains unit test.

[KevinJoiner]

Closing in favor of #262 and #288