[comm-lib] Let BlobServiceClient accept service-to-service token

Summary:
Updated `BlobServiceClient` to accept service-to-service token requests. This means HTTP services that rely on this Blob client, can accept service-to-service token and pass it through to Blob Service.

In short, previously:
- `client -[CSAT]-> backup -[S2SToken]-> blob` was possible
- `identity -[S2SToken]-> backup -[S2SToken]-> blob` wasn't possible

This diff makes the latter possible too, by overriding the [[ https://github.com/CommE2E/comm/blob/d6b19bfe9914869e4eb8b2a99d6cb9fc0afb6686/shared/comm-lib/src/http/auth_service.rs#L31 | accepts_services_token() ]] for BlobServiceClient.

Test Plan: Ran Backup and Blob locally, supplied Backup request with service-to-service token instead of CSAT, made sure the `COMM_SERVICES_DISABLE_CSAT_VERIFICATION` is disabled. Request succeeded.

Reviewers: kamil, will, varun

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D13318

shared/comm-lib/src/blob/client.rs

@@ -415,4 +415,8 @@ impl crate::http::auth_service::HttpAuthenticatedService for BlobServiceClient {
   ) -> Self {
     self.with_authentication(auth_credential)
   }
+
+  fn accepts_services_token(&self, _req: &actix_web::HttpRequest) -> bool {
+    true
+  }
 }