slow db due to huge instance_actions tables

[Max]

Description
===========
In a large environment the instance_actions and instance_actions_events tables for not deleted instances can grow infinitely.
For example when doing many migrations/live-migrations the events will sum up.
Every migration produces one action with ~10 events.

Huge tables in combination with the api autojoins can produce slow queries.

Keeping migration events for one month is usually enough.

The patch in the attachment proposes a clean_events option for the nova-manage command.

Steps to reproduce
==================
Have many VMs and instance actions e.g. live-migrations

Expected result
===============
fast api & db queries

Actual result
=============
slow api & overloaded db due to many entries in instance_actions and
instance_actions_events - normmallymax_statement_time

Environment
===========
nova zed
Regulary updating all hypervisors -> which means migrate VMs away
-> instance-actions/-events tables grow

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/nova/+/916927