Adding links + descriptions for MongoDB Atlas and MongoDB Vector Search (related to https://github.com/spring-projects/spring-ai/issues/456).

Thank you for taking time to contribute this pull request! You might have already read the [contributor guide][1], but as a reminder, please make sure to:

  • Sign the contributor license agreement
  • Rebase your changes on the latest main branch and squash your commits
  • Add/Update unit tests as needed
  • Run a build and make sure all tests pass prior to submission

Comment From: sobychacko

Merged via https://github.com/spring-projects/spring-ai/commit/fe3097ebf069f9c146b984da42d93bb82bff7871.