Java: Add Agents API consistent with .NET Agents/Abstractions (Beta release)

Implement the Semantic Kernel for Java Agents API, following the reference implementation in .NET.

The following work needs to be complete to get to a "Beta" status:

Microsoft.SemanticKernel.Agents.Core

Add this package to bring the core functionality online.

This will get us the "hero path" which is to provide a code sample to create an Agent that uses the ChatCompletion functionality already in the SK.
- Prioritize classes marked as "Experimental" as last to be done.
Add further agent support in the Core functionality experience.
- Azure AI (Foundry) agents
  - Foundry for Java not ready yet, but it's planned
  - NOTE: Foundry agent in .NET is still called the Azure AI agent.
- other agents
- Bedrock (should be done absolutely last, very difficult to work with.)

Add the agents abstractions to this package.

Small fixups throughout that will support Agents and that will bring us into further parity with the reference (.NET) implementation.

Restarting this workstream and targeting a beta release by May 1, 2025.

MCP integrations with SK are a "big deal" and the integration is quite simple/trivial. Will be a quick win.
- Blog posts:
  - MCP integration in Semantic Kernel for Java
Weslie was working through an ADR as this GA push was going on, but the truth remains in the code.
- A lot of what we are doing is also laying groundwork for adding memory to threads, so some of the reasons behind what we are doing may not be immediately obvious until we add the memory piece, e.g. notifying threads of all new messages and some threads doing nothing with those messages (for now).
- This is really a memory ADR, that ended up straying into the common agent invocation side of things, since this became a pre-requisite for memory. The code is definitely the source of truth though and the ADR is still mostly focussed on memory.
  - The ADR documents a lot of ideas, but certainly requires a lot more work. That said, feel free to take a look if useful:
    https://github.com/westey-m/semantic-kernel-1/blob/agent-memory-explore/docs/decisions/00NN-agents-with-memory.md