THREESCALE-11500: Fix confusing design flaw in "promote" UI

This issue exposes two problems, this PR deals with the first part:
"The Promote button is not enabled immediately when changes are done. Instead a job is enqueued and the button is enabled when this job is executed."

With the help of @jlledom, we've reached to the conclusion that not knowing when a job is going to be executed is a problem here. In this PR, we're removing the job who deals with updating proxy_configs_affecting_changes table and, instead, we propose to update the table directly at the ProxyConfigEventSubscriber. We don't think this will imply any substantial downgrade in the performance but we're open to discussion.

Verification steps

1. Go to Products > Integrations
2. Make a change there, could be adding a Mapping Rule or modifying the Policies, for example
3. Go to Integrations > Configuration and confirm the Promote button is enabled