Motivation:

Each time a aai access token is needed, we need to authenticate
again to obtain a new access token. However, this is not necessary
since we can use the refresh token, provided one is available
to obtain a new access_token.

Modification:

- initialise OAuth2AuthorizedClientService by using constructor
    instead of autowiring
- add a GET controller and a link that can be use to get the
    refresh token
- add to the list of scope `offline_access` to request for the
    refresh token from the auth server (that is Helmholtz AAI server).

Result:

Refresh token can now be obtain

Target: master
Review-at: https://gitlab.hzdr.de/hifis-technical-platform/helmholtz-marketplace-server/-/merge_requests/12