Changed block node endpoint type to a repeated value.

* This allows an operator to register a single endpoint with multiple block node APIs.

Signed-off-by: Joseph S. <121976561+jsync-swirlds@users.noreply.github.com>

Author: jsync-swirlds

HIP/hip-1137.md

@@ -255,7 +255,7 @@ message RegisteredServiceEndpoint {
          * <p>
          * This field is REQUIRED.
          */
-        BlockNodeApi endpoint_api = 1;
+        repeated BlockNodeApi endpoint_api = 1;
 
         /**
          * An enumeration of well-known block node endpoint APIs, and a