[keyserver] Authorize blob service requests

Summary:
Resolves ENG-6287.
Added Authorization header to blob service requests.

Test Plan:
Called all these blob functions in "main" keyserver.js. In blob service handlers, I added the following:

#[instrument(name = "assign_holder", skip(service))]
pub async fn assign_holder_handler(
  // ...
  auth: comm_lib::auth::AuthorizationCredential,
) -> actix_web::Result<HttpResponse> {
  info!(?auth, "Assign holder request");
  // ...

And checked the logs to see that the auth struct was populated with the correct data from the keyserver.

Reviewers: tomek, marcin, michal

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D10908