[Feature Request]: Mayday data source connector

Self Checks

• I have searched for existing issues search for existing issues, including closed ones.
• I confirm that I am using English to submit this report (Language Policy).
• Non-english title submitions will be closed directly ( 非英文标题的提交将会被直接关闭 ) (Language Policy).
• Please do not modify this template :) and fill in all the required fields.

Is your feature request related to a problem?

We use Mayday (https://www.mayday.fr) as our knowledge management platform for customer support. Today there is no way to sync its content into RAGFlow automatically. We have to export it and re-upload it by hand, and the dataset goes stale between exports.

The generic REST API connector can't be used as a workaround: the Mayday API only supports the OAuth 2.0 Client Credentials grant (short-lived JWT access tokens that must be refreshed), and the REST API connector only supports static `bearer`, `api_key_header` and `basic` auth. See #<ISSUE_A_NUMBER>.

Describe the feature you'd like

A dedicated connector in common/data_source/, following the pattern of the existing ones (e.g. Zendesk / Notion), which could also map Mayday-specific metadata (titles, collections, languages).

Describe implementation you've considered

No response

Documentation, adoption, use case

Additional information

No response