[CAP] Abstraction of actor_connector to go along with runtime factory and runtime abstraction

[rajan-chari]

Why are these changes needed?

AutoGen CAP comes with a default runtime, that's ready to use out of the box, to make it easy to start building Agents in minutes. However, different use cases and environments may require their own runtimes to host AutoGen CAP Agents. Runtime factories were added to make it easy to create new runtimes.

Along with runtime factories runtimes were also abstracted so that Agents/Actors can switch to different runtime implementations as needed.

This PR introduces and abstraction for agent connectors since they will depend on the needs of each runtime. Default implementation is also provided to make it super easy to start building Agents with AutoGen CAP.

Related issue number

Checks

• [x] I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• [x] I've added tests (if relevant) corresponding to the changes introduced in this PR.
• [x] I've made sure all auto checks have passed.

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[rysweet]

Hi Rajan, we've rebased and updated the branch for you. If you are still considering bringing this PR forward please go ahead and update and mark as ready for review. You may also consider having a closer look at 0.4 which has moved to an event-driven actor model. If you are not going to finish this PR please go ahed and close it.

[rajan-chari]

Hi Rajan, we've rebased and updated the branch for you. If you are still considering bringing this PR forward please go ahead and update and mark as ready for review. You may also consider having a closer look at 0.4 which has moved to an event-driven actor model. If you are not going to finish this PR please go ahed and close it.

Hi Ryan, I will update the PR and mark it as ready for review in a short while.