Disable IPv6 for GCS upstream resolver (#22)

DNS lookups for storage.googleapis.com will randomly result in IPv4 or IPv6 addresses, however our clusters currently only support IPv4 for egress traffic from pods. Therefore, switch off IPv6 for those resolvers.
https://nginx.org/en/docs/http/ngx_http_core_module.html

root-files/opt/flownative/lib/nginx-legacy.sh

@@ -227,7 +227,7 @@ EOM
     }
     # pass persistent resource requests to the custom endpoint (S3, Minio, GCS ...)
     location ~* "^${BEACH_PERSISTENT_RESOURCES_BASE_PATH}([a-f0-9]{40})/" {
-        resolver ${BEACH_ASSET_PROXY_RESOLVER};
+        resolver ${BEACH_ASSET_PROXY_RESOLVER} ipv6=off;
         proxy_set_header Authorization "";
         add_header Via 'Beach Asset Proxy';
         ${addHeaderStrictTransportSecurity}
@@ -244,7 +244,7 @@ EOM
     }
     # pass persistent resource requests to GCS
     location ~* "^${BEACH_PERSISTENT_RESOURCES_BASE_PATH}([a-f0-9]{40})/" {
-        resolver ${BEACH_ASSET_PROXY_RESOLVER};
+        resolver ${BEACH_ASSET_PROXY_RESOLVER} ipv6=off;
         proxy_set_header Authorization "";
         add_header Via 'Beach Asset Proxy';
         ${addHeaderStrictTransportSecurity}
@@ -266,7 +266,7 @@ EOM
         set \$assetUri ${BEACH_PERSISTENT_RESOURCES_FALLBACK_BASE_URI}\$1;
         add_header Via 'Beach Asset Fallback';
         ${addHeaderStrictTransportSecurity}
-        resolver ${BEACH_ASSET_PROXY_RESOLVER};
+        resolver ${BEACH_ASSET_PROXY_RESOLVER} ipv6=off;
         proxy_pass \$assetUri;
     }
 EOM