Description of problem:

In Administer -> Settings, a setting that is read-only by default - "Foreman URL" - is displayed with an "edit" button. On clicking it, the field actually becomes editable and after changing (to something valid) and confirming with a check mark icon, I get error "Error updating setting: undefined" in the WebUI.

foreman-tail says: "Backtrace for 'Action failed' error (ActiveRecord::ReadOnlyRecord): Setting is marked as readonly" + traceback

How reproducible:

Deterministic, reproduced on nightly

Is this issue a regression from an earlier version:

Yes

Steps to Reproduce:

1. Have a Satellite

2. Administer -> Settings

3. Change Foreman URL to some valid URL

Actual behavior:
Error, traceback

Expected behavior:
It shouldn't have been possible to edit this in the first place