[Docs] Resolve Broken Links in Documentation

[harishmohanraj]

Why are these changes needed?

This PR addresses the issue of broken links in the documentation by updating or removing invalid links and replacing them with correct ones.

Changes Made

• Fixed ~ 200 broken links identified using muffet CLI.
• Updated links to point to valid resources or removed outdated links where no replacement was available.
• Added a GitHub workflow which checks for broken links after the mintlify deploy is successful

Related issue number

Closes #301

Checks

• I've included any doc changes needed for https://docs.ag2.ai/. See https://docs.ag2.ai/docs/contributor-guide/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.