Extend operator headers

[Razz4780]

Closes #2466

CLI version and user name/hostname headers are sent with all operator requests.
Client certificate header:

1. mirrord operator status: we don't know operator license fingerprint before getting the resource, so header is not sent.
2. mirrord exec: as soon as we get the operator resource, we prepare the client cert header. If we fail, command aborts.
3. mirrord ls / mirrord operator session: as soon as we get the operator resource, we try to prepare the client cert header. If we fail, we continue without it

I kind of went full aggro on the operator client code and made more changes than necessary :V

1. Copied to mirrord ls the extra discovery step present in mirrord exec (Improve operator discovery UX (CLI) #2487)
2. Moved some parts of operator client code to new separate submodules (errors, http upgrade request logic, connection wrapper, operator discovery)
3. Unified format of progress messages

[aviramha]

We don't want a license to be needed for the non actual usage APIs. It should be fallible and optional.

[Razz4780]

We don't want a license to be needed for the non actual usage APIs. It should be fallible and optional.

Do you mean operator license or user license?

[aviramha]

We don't want a license to be needed for the non actual usage APIs. It should be fallible and optional.

Do you mean operator license or user license?

I meant user license but we shouldn't check the operator license for getting it's status anyway

[Razz4780]

We don't want a license to be needed for the non actual usage APIs. It should be fallible and optional.

Do you mean operator license or user license?

I meant user license but we shouldn't check the operator license for getting it's status anyway

So, summarizing:

1. operator status -> no check at all, plain GET with version/name/hostname headers
2. target connection -> operator license validity check, user license required
3. session management or listing targets -> no operator license validity check, fallible and optional user license

Correct?

[aviramha]

I'd add the user license to the status too, just make it optional.

[DmitryDodzin]

I think operator api can be a changed bit to prevent any issues that may happen post future changes

[DmitryDodzin]

I would double check that the progress bar isn't a bit much but other than that looks good =]