Transport refactor

[dwoz]

What does this PR do?

Refactor transports to make them more plug-able. This PR adds the concept of channels to salt. Channels handle specifics related to salt such as message structure, authentication, ect. Transports are simplified to only handle sending and receiving messages over the wire.

What issues does this PR fix or reference?

Fixes: #61161
Superseeds: #60867

Merge requirements satisfied?

• Docs
• Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• Tests written/updated

Please review Salt's Contributing Guide for best practices.

See GitHub's page on GPG signing for more information about signing commits with GPG.

[waynew]

One typo left here, there was another typo I missed last time:

creates and runs an it's own ioloop.

probably should be

creates and runs it's own ioloop.

(or runs in it's own ioloop 🤷 )

Entirely non-blocking, of course 👍

[github-actions]

Hi! I'm your friendly PR bot!

You might be wondering what I'm doing commenting here on your PR.

Yes, as a matter of fact, I am...

I'm just here to help us improve the documentation. I can't respond to
questions or anything, but what I can do, I do well!

Okay... so what do you do?

I detect modules that are missing docstrings or "CLI Example" on existing docstrings!
When I was created we had a lot of these. The documentation for these
modules need some love and attention to make Salt better for our users.

So what does that have to do with my PR?

I noticed that in this PR there are some files changed that have some of these
issues. So I'm leaving this comment to let you know your options.

Okay, what are they?

Well, my favorite, is that since you were making changes here I'm hoping that
you would be the most familiar with this module and be able to add some other
examples or fix any of the reported issues.

If I can, then what?

Well, you can either add them to this PR or add them to another PR. Either way is fine!

Well... what if I can't, or don't want to?

That's also fine! We appreciate all contributions to the Salt Project. If you
can't add those other examples, either because you're too busy, or unfamiliar,
or you just aren't interested, we still appreciate the contributions that
you've made already.

Whatever approach you decide to take, just drop a comment here letting us know!

Detected Issues (click me)

Check Known Missing Docstrings...........................................Failed
- hook id: invoke
- duration: 1.75s
- exit code: 1
The function 'recv' on 'salt/modules/cp.py' does not have a 'CLI Example:' in it's docstring

The function 'recv_chunked' on 'salt/modules/cp.py' does not have a 'CLI Example:' in it's docstring

The function 'envs' on 'salt/modules/cp.py' does not have a 'CLI Example:' in it's docstring

Found 3 errors

---

Thanks again!