config: allow overriding rpc and pub/sub labels

[VDanielEdwards]

Subject

This PR implements an extension to the participant configuration that allows to override the labels of DataPublisher, DataSubscriber, RpcClient, and RpcServer controllers in the participant configuration.

The format (all other controllers analogous) is like this:

RpcClients:
  - Name: MyRpcController
    Labels:
      - Key: SomeKey
        Value: SomeValue
        Kind: Mandatory
      - Key: AnotherKey
        Value: AnotherValue
        Kind: Optional

The labels completely replace what is specified in the code.

This is just a proposal to play around with, it is not neccessarily the final form.

JIRA Issue SILKIT-1636

Instructions for review / testing

Developer checklist (address before review)

• [x] Changelog.md updated
• [ ] Prepared update for depending repositories
• [x] Documentation updated (public API changes only)
• [ ] API docstrings updated (public API changes only)
• [ ] Rebase → commit history clean
• [x] Squash and merge → proper PR title