The following re-works the common leadership pinning API. It removes the
idea that the API is part of a facade and instead defines it's own type,
one that can move independantly of a facade version. This has been an
ongoing discussion for sometime, but has concretely formalised to a
discourse post[1].

The changes are relatively simple, adding new methods for taking a
application name slice, so calling Pin/Unpin doesn't require a machine
to talk to. This should give us a lot of flexibility about when and how
we can call these methods.

1. https://discourse.juju.is/t/common-facade-apis/3081

The tag is required to be higher up the stack in-order to make it
accessible for external calls to change it depending on their
requirements.

The following updates the methods to be a lot more generic as we
no-longer care about if it's a machine we're dealing with. All we care
about is the application names, so with this in mind I've updated the
type correctly, along with tests...

…p-pinning-type

juju#11631

## Description of change

The following re-works the common leadership pinning API. It removes the
idea that the API is part of a facade and instead defines its own type,
one that can move independently of a facade version. This has been an
ongoing discussion for some time, but has concretely formalised to a
discourse post[1].

The changes are relatively simple, adding new methods for taking an
application name slice, so calling Pin/Unpin doesn't require a machine
to talk to. This should give us a lot of flexibility about when and how
we can call these methods.

1. https://discourse.juju.is/t/common-facade-apis/3081

## QA steps

Test pass, this is a mechanical refactoring change

## Bug reference

https://bugs.launchpad.net/juju/+bug/1879663

During a destruction of a machine application, we should attempt to
remove any last references to ties for leadership pinning.

The normal destroy flow will attempt to remove the leadership pinnings,
but will fail if there exists pinnings. Using force will allow this to
proceed.

The call for removing pinnings is idempotent, so calling it multiple
times is fine.

…n-destroy' into port-stickupkid/unpin-machine-applications-on-destroy