Support GitLab configuration with private access token

Hi everyone!

According to the GitLab documentation you can read repositories with a private access token. See link:
https://docs.gitlab.com/ee/api/README.html#personalproject-access-tokens

The current version and prior version of Spring Cloud Config Server seem not to support this feature.

Environment

Component       Version
Spring Boot     2.4.0
Spring Cloud    2020.0.0-M5
GitLab CE       13.5.3
Java VM         openjdk 11

What I have tried so far
I have created a private access token on the GitLab server and tried to configure it inside the spring cloud config server.

1. When I add the ?private-token= parameter, the server won't start because JGit seems to append a path to the configured uri which leads to an invalid url.
   Caused by: org.apache.http.client.CircularRedirectException: Circular redirect to 'https://gitlab.home.local/spring-cloud-config.git?private_token=<token>/info/refs&service=git-upload-pack'
2. I have tried to add the token as a header field in the application.properties. But the property seems to be ignored or at least not evaluated at this point.
   spring.cloud.config.headers.PRIVATE-TOKEN=<token> or
   spring.cloud.config.headers.Authorization=Bearer <token>

Best regards,
David

Start by reproducing the GitLab repository access failure with the private-token URI and the two application.properties header configurations described in the issue. Trace how Spring Cloud Config Server passes the repository URI and credentials to JGit, then verify that a private GitLab repository can be read without the malformed URL or ignored authentication settings.