Fixes #36597 - Rename 'Change content source' job template

[jeremylenz]

What are the changes introduced in this pull request?

The user was confused because running the job template on the host didn't change the host's content source. In actuality, it updates subscription-manager configuration on the host based on the host's current content source. It's meant to only be run just after changing the content source on the server, as part of the 'Change Content Source' feature.

So, the changes here are

1. Change the name of the job template Change content source to Configure host for new content source. This reflects what the job template actually does. Includes a DB migration similar to https://github.com/theforeman/foreman/blob/develop/db/migrate/20220204155632_rename_job_report_template.rb (thanks for the tip @ianballou)
2. Change the name of the method change_content_source to configure_host_for_new_content_source
3. Rename files accordingly
4. Add (hopefully) helpful comments to the job template

Considerations taken when implementing this change?

I didn't update the name of the remote execution feature, since that would require a code change in foreman_remote_execution.

What are the testing steps for this pull request?

Run migrations:

bundle exec rails db:migrate

Run seeds and restart the server:

bundle exec rails runner "ForemanInternal.all.first.destroy" && bundle exec foreman start

Test the following:

1. In Hosts > Job Templates, verify that the "Change content source" template is gone and the new "Configure host for new content source" template is there.
2. test changing a host's content source and verify everything still works I guess

[theforeman-bot]

Issues: #36597

[jeremylenz]

I changed the ERB comments to regular Bash comments.

See theforeman/foreman_remote_execution#822

[ianballou]

Code is looking fine, now I just need to actually test it.

[ianballou]

Working for me! I tested the case of having a same-named job template already and it was backed up properly. New template works as well.