feat(integration-link-create): better catch 401 from SCM API

[EtienneM]

$ scalingo -a dadazdazdazdaz integration-link-create https://gitlab.com/Moi/repo --auto-deploy --branch master
 !     Fail to create SCM repository integration: the SCM API returned a 401 error.
 !     Did you revoked the Scalingo token from your profile? In such situation, you may want to remove and re-create the SCM integration.
 !     
 !     The complete error message from the SCM API is: Request forbidden (403): {error: invalid_token}, {error_description: Token was revoked. You have to re-authorize from the user.}

• Add a changelog entry in the section "To Be Released" of CHANGELOG.md