[JUJU-3887] Avoid removing the track if set to latest in channel normalization

[cderici]

Description

This is essentially a backport of a fix we already have in the master branch. In the past we used to remove the latest track from the origin channel as part of the normalization even if it's set by the user via the --channel flag. Now we're passing it through into the ResolveCharm.

Fixes #863

QA Steps

We can directly use the scenario in #863

python -m asyncio
asyncio REPL 3.10.6 (main, Mar 10 2023, 10:55:28) [GCC 11.3.0] on linux
Use "await" directly instead of "asyncio.run()".
Type "help", "copyright", "credits" or "license" for more information.
>>> import asyncio
>>> from juju import model; m=model.Model(); await m.connect();await m.deploy("postgresql-k8s",series="focal", channel="latest/stable")
<Application entity_id="postgresql-k8s">
>>>

[juanmanuel-tirado]

LG2M

I have checked and this is already in 3.1 and master branches.