Consistent PMM Server log management

As a result of issues such as PMM-7464 the log files for NGINX can grow out of control, e.g.

$ du -sh /srv/logs/nginx.error.log 
13G     /srv/logs/nginx.error.log

The log managed by supervisord is already controlled, but the ones left to NGINX are not.

Suggested fix:

• add log rotation to allow log control

Implementation:

• add log rotation
• delegate log rotation to exclusively to supervisord
• redirect all nginx logs to /stdout and /stderr vs to log files

How to test:

• there are automated tests, which should be green:
  https://github.com/Percona-Lab/pmm-api-tests
  https://github.com/percona/pmm-managed
• get inside of the PMM docker container and verify that the `/srv/logs` file list is limited to the following:
  • a fresh install wouldn't have the files, deleted by this PR
  • a PMM Server upgraded from an older version to this one would still have those files, but this is impossible to test

Example of a PMM Server latest version: