[Patching][Doc] Patching doc lacks the description of internals/architecture

[Irina Povolotskaya]

Currently, we have end-user doc on how to apply patches [1].

Nevertheless, we don't have a document that would:
- give a deeper insight into the patching internals (repos, status)
- serve as an FAQ for plugin developers to estimate the impact maintenance updates might have for their plugins

So, the following issues should be covered in the Operations Guide under a new section:
- what is patching
- where to find info on bugfixes that will enter MU (e.g. where in LP they're tracked? where're they documented? errata is WIP now for example)
- how often MU are released
- what repos are used and what status they might enter
- where developers can get notification on MU (they should know they can fill in the form and get a notification at least when MU are released)

I can provide a design doc with more details to create a summary section in OpsGuide that would
answer these questions.

[1] https://docs.mirantis.com/openstack/fuel/fuel-6.1/operations.html#applying-patches

[Evgeny Konstantinov (evkonstantinov)]

We now have MU docs released with each MU, e.g. https://docs.mirantis.com/openstack/fuel/fuel-7.0/maintenance-updates.html

This should cover the reqs in this bug ticket. Feel free to reopen if you think more info is necessary.