[PP-1] Add message on the status report that a background update is currently in progress

Problem/Motivation

Follow-up to #3357969: For web server dependent unattended updates run the entire life cycle in a separate process that will not be affected by hosting time limits where we were going to add this. We didn't add it because getting status of a process by a PID is complicated

We also have to consider when want to put the message on the status report. In #3357969: For web server dependent unattended updates run the entire life cycle in a separate process that will not be affected by hosting time limits we were adding the message after we got the update release version but at the start of the update process(begin()). Maybe we should want to till apply() because it is more likely to actually complete at that stage.

Steps to reproduce

Proposed resolution

Add a message that a background update is process on the status report.

Remaining tasks

Where else would we want this message? On the update form so the user doesn't try to start another 1?

User interface changes

API changes

Data model changes