feat: Authorization header to prometheus queries

[jpinsonneau]

Read the Authorization header and set it on prometheus calls when possible to allow multitenancy and handle roles at prometheus level.

When not specified, the default client is used, coming from the configuration file provided.

I gave a try with the openshift example provided in #37 removing the authorization config from the file.

• When providing a header I can access to the metrics:

• When providing a wrong header or no header I get a 401 error:

Partially fixes #13