Adds Redis Memory extension class

[justin-cechmanek]

Why are these changes needed?

This PR adds the RedisMemory class to allow for developers to use Redis vector search for agent memory. Redis vector db offers a persistent store and the ability to semantically search for relevant memories.

Related issue number

None

Checks

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

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[ekzhu]

Thanks for the PR. A couple of things:

1. Let's use the module path autogen_ext.memory.redis for the new module.
2. Add API doc to RedisMemory with examples of usage. Make sure the code blocks are checked by pyright, the CI checks the formatting and types of API docs. See python/README.md for information on checks. Many users use the API Reference directly.
3. In the usage guide notebook, can you simplify the setup instructions for the redis example. The example should just refer to the API doc using reference:

{py:class}`~autogen_ext.memory.redisvl.RedisMemory`