Manage all PMM Server logs with supervisord

We manage logs of most PMM Server components with supervisord. Currently, there is one exception: nginx which manages its logs on its own with configurations in three different places.

We should change its configuration to log to stderr and manage its logs with supervisord as we do for every other component.

Should we do it via Ansible templates in pmm-update instead of sed? (see https://github.com/Percona-Lab/pmm-submodules/blob/f602d81bba2e94e2664ad63a2206ed9052df899a/build/bin/build-server-rpm#L188)