Fix UX around enabling the Change Requests feature

The Change Requests screen (screenshot below) comes with an info note that says:

> To enable this feature set a minimum number of approvals in _Environment Settings_

However, clicking "Environment Settings" in that note leads to a page (frontend: `/project/.../environment/.../settings`) without any obvious "minimum number of approvals" element immediately visible in the UI (screenshot below). However, when clicking to enable "Change Requests", the "Minimum number of approvals" field shows up.


After enabling the Change Requests toggle:

The suggestion is to improve both the UI element and text:
- The current UI element is a _collapsible_ note, which does not provide the right emphasis to its content. We should decide on a better UX to let users know they have to do something in settings before using the Change Requests feature.
- The note is gone as soon as the Change Requests toggle is enabled in the Environment Settings page, even if the "minimum number of approvals" is still zero, leading to a blank non-functional Change Requests page.
- The text should be fixed to something that resembles:
> You must enable Change Requests in _Environment Settings_ before using this feature.

IMO referring to "minimum number of approvals" should be closer to the toggle instead of the Change Requests page. e.g. add a helper text close to the number input that's currently just red.
- The _Environment Settings_ form can be saved even if "Change Requests" is enabled but "Minimum number of approvals" is zero.
- Deleting the current number in the input disables the feature and hides the text input. One must only use the arrow buttons and that's annoying UX.