Addressing feedback before agenthub GA launch.

[shenoyvvarun]

Description

• Renamed/moved many files from examples/agenthub/openai/... to examples/agenthub/... (agents, responses, tools, memory, mcp, vector stores, etc.).
• Added: examples/agenthub/responses/use_google_gemini_model.py
• Modified: README.md to include licenses, contributing and security.
• Remove before you start section on how to create api-keys
• Switched to xai model from gpt model where possible.

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Tested by running examples

Test Configuration:

• Firmware version:
• Hardware:
• Toolchain:
• SDK:

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules