Add further installation guidance and files for CaptainAgent

[marklysze]

Why are these changes needed?

The notebook documentation for CaptainAgent advises to install via pip install ag2[autobuild], this should be pip install ag2[captainagent]. Furthermore, the blog post doesn't provide any guidance, so I've added a quick note.

Also, the default tools library for CaptainAgent is not being included with the pip install, so have added this so it will be installed when using pip install ag2 (can't be specific to extras).

Have also corrected the code on the blog, minor import issue, as well as changing the model in the sample code to GPT-4o as it was noted that this was more reliable.

For the pysqlite3 installation issue:
Instead of installing pysqlite3, it will now install pysqlite3-binary which does not require building of pysqlite3. When running the code after a test pip install, I could see that this binary version creates both a pysqlite3 and pysqlite3-binary site-package folder, both with the compiled binary. Running a sample code and stepping through shows that pysqlite3 is being detected and used.

If others can test with a pip install using this branch and testing CaptainAgent that would be great:

1. Create a virtual environment (e.g. conda create -n ...)
2. Enter the virtual environment (e.g. conda activate ...)
3. After cloning the branch, go into the root folder of the code
4. Run pip install -v ".[captainagent]"
5. Make sure that the ...site-packages/autogen folder (find the site-packages folder through pip show ag2) has the CaptainAgent 3 tools sub-folders and files (.../autogen/agentchat/contrib/captainagent/tools/...)
6. Run a sample program (e.g. from the blog) and make sure it runs through okay

Related issue number

N/A

Checks

• I've included any doc changes needed for https://ag2ai.github.io/ag2/. See https://ag2ai.github.io/ag2/docs/Contribute#documentation 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.

Fixes #82