[RFE] Add a memory profiler

[Rodolfo Alonso]

This RFE proposes to add a memory profiler plugin in Neutron. This plugin could be enabled to periodically log and report the Neutron server memory consumption.

In https://review.opendev.org/c/openstack/neutron/+/803034 I present a draft of what this plugin could be:
- It will periodically report the current and max memory consumption.
- It will also report the modules with the biggest memory growth.
- It is configurable: the reporting period, the max number of modules and the module patter (to filter only by a set of modules to track).

By default, this plugin is disabled. This should be used only for debugging because it could affect to the performance.

[Slawek Kaplonski (slaweq)]

Let's discuss that rfe in the next drivers meeting on Friday 20.08.2021

[Slawek Kaplonski (slaweq)]

We discussed that RFE on the drivers meeting on 27.08.2021: https://meetings.opendev.org/meetings/neutron_drivers/2021/neutron_drivers.2021-08-27-14.00.log.html#l-108 and we decided to approve it. Please follow up with implementation now :)