feat(Auth): Added support for keycloak access_token

[TTalex]

Description

• Openfoodfacts api now supports access_token authentication using 'Authorization: Bearer <access_token>' header.
• This PR offers a third way to auth users (after username/password and session_cookie).

Testing

• I haven't added unit tests, since existing auth tests are mocked anyways
• Also, there seem to be differences in the way OFF environments handle the authorization header. The header is ignored in '.net' env, but works well in '.org' env.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[john-gom]

Looks good. It might be appropriate to flag the session cookie and username password as deprecated, but that could be done in a follow up PR.

@TTalex when testing on .net did you use a token from auth.openfoodfacts.net?