Different authorization for different targets, via relabel

[lapo-luchini]

Is your feature request related to a problem? Please describe

It wold be nice to allow overriding ahtorization (in my case "bearer", but maybe in general) on a per-target basis instead of forcing that only at the job level, as it is cumbersome to have whole different jobs with different names for identical jobs with different targets.

- job_name: syncthing
  authorization:
    type: Bearer
    credentials: bearer1
  static_configs: 
  - targets:
    - host1:8384

- job_name: syncthing_2
  authorization:
    type: Bearer
    credentials: bearer2
  static_configs: 
  - targets:
    - host2:8384
    labels:
      job: syncthing

Describe the solution you'd like

- job_name: syncthing
  authorization:
    type: Bearer
  static_configs: 
  - targets:
    - host1:8384
    labels:
      __authorization_bearer__: bearer1
  - targets:
    - host2:8384
    labels:
      __authorization_bearer__: bearer2

Describe alternatives you've considered

No response

Additional information

I guess support should be added around here.

[fengxsong]

It would be nice if we could add some http headers via relabeling while scraping targets:)