Read GCP proxy EPP SSL secret from GCS

This allows us to not ship the proxy with certificates/private keys. The secret is still encrypted by KMS. Reading the secret only happens once when the first EPP request comes in, which should not incur any tangible performance penalty.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=191771680

java/google/registry/proxy/terraform/modules/input.tf

@@ -10,6 +10,9 @@ variable "gcr_project_name" {}
 # The base domain name of the proxy, without the whois. or epp. part.
 variable "proxy_domain_name" {}
 
+# The GCS bucket that stores the encrypted SSL certificate.
+variable "proxy_certificate_bucket" {}
+
 # Cloud KMS keyring name
 variable "proxy_key_ring" {
   default = "proxy-key-ring"