[native] Disable headerRight when the role name is empty

Summary:
In an effort to prevent the user from reaching a state that would result in an error (and just a general better UX overall), we should disable the headerRight 'Create' button when the role name is empty. We should allow a user to create a role without any selected permissions because on the keyserver, we add a set of guaranteed permissions anyways, so we won't end up with a case of a role with no permissions.

Error handling for duplicate role names / etc will be done in a later diff.

Part of ENG-4178

Depends on D8428

Test Plan:
Verified that the headerRight component is disabled when it should be, and enabled when the role name is non-empty.

Reviewers: atul, ginsu

Reviewed By: ginsu

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8430