docs: clarify CircleCI Personal API token setup

[TOGEP]

Summary

The DevLake CircleCI connector uses CircleCI API v2 endpoints for connection checks and data collection.
However, CircleCI's official documentation states that Project API Tokens are not supported for API v2.

https://circleci.com/docs/api/v1/#get-authenticated

We recommend using personal API tokens at this time because project API tokens are not supported for API v2.

Because the current wording could be interpreted as saying that Project API Tokens can also be used with DevLake,
this PR updates the CircleCI configuration docs to make it clear that DevLake expects a Personal API Token.

Does this close any open issues?

No related open issue found.

Screenshots

N/A

Other Information

• DevLake's CircleCI connector uses CircleCI API v2 endpoints, including:
  • /v2/me
  • /v2/me/collaborations
  • /v2/project/{slug}
  • /v2/project/{slug}/pipeline
  • /v2/pipeline/{id}/workflow
  • /v2/workflow/{id}
  • /v2/workflow/{id}/job

[TOGEP]

This is not directly related to the token type clarification,
but Ilearned from #8634 that CircleCI projects need to be followed by the token owner before they can be discovered in DevLake.

I included this small note here as a related documentation improvement.