SessMan: dedicated gRPC message types

[jamesturner246]

This is the first in a series of changes which will replace the existing generic gRPC messages (arbitrary data packed to any) to a simpler and more reliable system of purpose-built gRPC messages.

This first PR starts with the Session Manager. Next will come Process Manager and then Controller. There is a sister PR in the drunc repository required to run this (DUNE-DAQ/drunc#485).

One can test by running describe, list_all_sessions and list_all_configs on a connected Session Manager driver.

Benefits:

1. type safety is better. We know what a message's type is for free
2. No more Any-type packing and unpacking. This is inefficient and hard to follow.
3. We will be able to make better use of in-built gRPC features, such as authentication.

[wanyunSu]

Is there a documentation on how to start a Session Manager service and connect to it?

[jamesturner246]

At the moment, in our frontend testing we are just /usr/sbin/sshd && drunc-session-manager, and connecting to it via something like:

from drunc.session_manager.session_manager_driver import SessionManagerDriver
from drunc.utils.shell_utils import create_dummy_token_from_uname

def get_session_manager_driver() -> SessionManagerDriver:
    """Get a ProcessManagerDriver instance."""
    token = create_dummy_token_from_uname()
    return SessionManagerDriver(
        SESSION_MANAGER_URL, token=token, aio_channel=False
    )

Ed: No documentation now though. Do you want a note added somewhere?

[wanyunSu]

It would be good to start adding a Session Manager session in drunc wiki, similar to the PM: https://github.com/DUNE-DAQ/drunc/wiki/Process-manager

[jamesturner246]

Agreed. I will make a separate issue to tackle later though, so I can get these changes done quickly (I am mindful that work on the process manager will be starting soon, so I would prefer to finish before this time):

DUNE-DAQ/drunc#497

[PawelPlesniak]

Tested manually
Also passed MSQT, although is independent of tests ran there
LGTM