RUMM-1615 Create RUMCommandPublisher to publish RUM command to a subscriber

[maxep]

What and why?

Introduce the RUMCommandPublisher protocol to unify command publishers interface. This small refactoring prepares for the upcoming SwiftUI view handler.

How?

The RUMCommandPublisher enforce that any publisher implement the same method signature.

Review checklist

• Feature or bugfix MUST have appropriate tests (unit, integration)
• Make sure each commit and the PR mention the Issue number or JIRA reference

[ncreated]

Nice refactoring 👌. Even though RUMCommandPublisher is only a blueprint protocol (not much leveraged in testing and DI), I'm up for having this as that clearly embraces our convention around RUM commands processing 👍.

[buranmert]

lgtm but i didn't fully understand why we needed this for SwiftUI.?

[maxep]

@buranmert It is not needed for SwiftUI, but I found that the naming convention func subscribe(commandsSubscriber: RUMCommandSubscriber) didn't quite reflect the actual command flow (You don't subscribe to a subscriber). Here, I'm explicitly stating that a Publisher publish to a Subscriber, the protocol only unifies the interface of command publishers.