Check admin permission before able to manage config entries

[balloob]

Description:

Check that a user is part of the admin group before allowing changes to config entries.

We'll need to add such checks to all config APIs.

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.

If the code does not interact with devices:

• Tests have been added to verify that the new code works.