Disable confirm button when missing permission

Disable the confirm button while fetching permission. Re-enable button
when the user has permission to use direct access. If the user does not
have access, the button stays disabled.

Fixes: 477180283
Test: Updated
Change-Id: Id5aed26c24ab9413a76249bbeec838f506c23287
Presubmit-runs-per-test: //tools/studio/google/cloud/testing/directaccess:directaccess_tests@200