[terraform] Bump staging Blob to 1.2.0

Summary:
Includes new `/holders` endpoints and base64 support: stack of D13479 .. D13482 and D13503
Bumped semver minor because of these new endpoints
Git tag: https://github.com/CommE2E/comm/releases/tag/blob-v1.2.0

Test Plan: terraform plan

Reviewers: will, varun, ashoat, kamil

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D13510

services/terraform/remote/service_blob.tf

@@ -1,5 +1,5 @@
 locals {
-  blob_service_image_tag      = local.is_staging ? "1.1.3-staging" : "1.1.3"
+  blob_service_image_tag      = local.is_staging ? "1.2.0" : "1.1.3"
   blob_service_container_name = "blob-service-server"
   blob_service_server_image   = "commapp/blob-server:${local.blob_service_image_tag}"