Description of problem:
When changing the content source of a host, the UX of the change content source page implies that the change has been completed after selecting the options and clicking the 'Change content source' button, but it is necessary to take the additional step of running the provided remote execution (REX) job or shell script on the host to fully complete the change.

Version-Release number of selected component (if applicable):
Satellite 6.12.0

Steps to Reproduce:
1. Register a host to a Satellite that has at least one external Capsule.
2. In the web UI, navigate to Hosts > All Hosts > [hostname]
3. Click the vertical ellipsis icon next to the Edit button and select 'Change content source.'
4. Select an environment, a content view, and a content source from the lists.
5. Click the 'Change content source' button.

Actual results:
- A notification appears with the text 'Content source successfully updated' and a green check mark. 
- The 'What's next?' section on the page says 'Run job invocation to update configuration on all hosts,' which could mean 'all hosts other than the one that was just changed.'

Expected results:
The notification and 'What's next?' section make it clear that the change will not be completed until the REX job or the script is run on the host. The text of the 'Change content source' button is changed to reflect the fact that clicking it will not fully complete the content source change.