SessMan: dedicated gRPC message types

[jamesturner246]

Resolves DUNE-DAQ/drunc_ui#496

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 druncschema repository required to run this (DUNE-DAQ/druncschema#58).

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.

[PawelPlesniak]

This looks good, but just to clarify the OldDescription object is a placeholder until all of the Description objects are corrected to the actual object they are describing with individual 'Description' objcets in the respective .proto, right?

[jamesturner246]

Correct. OldDescription is transitional until all services use the new Description.

Ed. Well actually I will use the same Description type across all, since they all will be identical. No point duplicating.

[PawelPlesniak]

Tested by running a drunc_session_manager in one shell, and in an interactive python shell ran

>>> from drunc.session_manager.session_manager_driver import SessionManagerDriver
>>> from drunc.utils.shell_utils import create_dummy_token_from_uname
>>> token = create_dummy_token_from_uname()
>>> d = SessionManagerDriver(address="localhost:50000", token=token, aio_channel=False)
>>> d.describe()
type: "session_manager"
name: "session_manager"
session: "session_manager"
commands {
  name: "describe"
  data_type: "None"
  help: "List the methods exposed by this endpoint."
  return_type: "description_pb2.Description"
}
commands {
  name: "list_all_sessions"
  data_type: "None"
  help: "List all active sessions."
  return_type: "session_manager_pb2.AllActiveSessions"
}
commands {
  name: "list_all_configs"
  data_type: "None"
  help: "List all available configurations."
  return_type: "session_manager_pb2.AllConfigKeys"
}

>>> d.list_all_sessions()
name: "session_manager"
active_sessions {
  name: "dummy_session"
  user: "dummy_user"
  config_key {
    file: "dummy_config_file"
    session_id: "dummy_config_session_id"
  }
}

>>> d.list_all_configs()
name: "session_manager"
config_keys {
  file: "example-configs.data.xml"
  session_id: "local-tpreplay-config"
}
config_keys {
  file: "example-configs.data.xml"
  session_id: "local-crt-bern-1x1-config"
}
config_keys {
  file: "example-configs.data.xml"
  session_id: "local-crt-grenoble-1x1-config"
}
config_keys {
  file: "example-configs.data.xml"
  session_id: "local-2x3-config"
}
config_keys {
  file: "example-configs.data.xml"
  session_id: "local-1x1-config"
}
config_keys {
  file: "example-configs.data.xml"
  session_id: "ehn1-tpreplay-config"
}
config_keys {
  file: "example-configs.data.xml"
  session_id: "ehn1-local-2x3-config"
}
config_keys {
  file: "example-configs.data.xml"
  session_id: "ehn1-local-1x1-config"
}
config_keys {
  file: "lrSession-r.data.xml"
  session_id: "lr-session"
}
config_keys {
  file: "lrSession-v.data.xml"
  session_id: "lr-session"
}
config_keys {
  file: "lrSession-singleapp.data.xml"
  session_id: "lr-session"
}
config_keys {
  file: "lrSession-separate.data.xml"
  session_id: "lr-session"
}
config_keys {
  file: "lrSession.data.xml"
  session_id: "lr-session"
}
config_keys {
  file: "lrSession-g.data.xml"
  session_id: "lr-session"
}
config_keys {
  file: "lrSession-gg.data.xml"
  session_id: "lr-session"
}
config_keys {
  file: "timing.data.xml"
  session_id: "test-session"
}
config_keys {
  file: "appSession.data.xml"
  session_id: "test-session"
}

[PawelPlesniak]

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