Handle metadata for get_configuration and subscribe_configuration

[blackwood-ra]

This PR would address #117

Adds a metadata parameter to the client's existing get_configuration and subscribe_configuration implementations. The new metadata parameter matches existing function signatures (from get_state, for example).

Callers would need to include optional metadata:

let mut stream = client
  .subscribe_configuration(CONFIGSTORE_NAME, vec![(&key)], None)
  .await?;

[cscetbon]

As far as I understand the release process follows the one from the main repo, so I don't think we should upgrade it here.

[blackwood-ra]

Okay. I wasn't sure what the version management rules were. I can revert this change to the version.

[cscetbon]

tbh I'm learning as well. I suppose that's how it works even if I saw @danielgerlag's PR changing it. I would say we don't know in which version it will go so a PR shouldn't change it, especially you could have x PRs in parallel.

[yaron2]

We can accept this for the upcoming release

[yaron2]

@cscetbon please revert to 0.14.0

[blackwood-ra]

@yaron2 @cscetbon Reverted to 0.14.0

[cscetbon]

@cscetbon please revert to 0.14.0

Not mine though 😬