add cors headers to http proxy

src/test/groovy/io/emeraldpay/dshackle/config/ProxyConfigReaderSpec.groovy

@@ -83,6 +83,8 @@ class ProxyConfigReaderSpec extends Specification {
         act.port == 8080
         act.preserveBatchOrder
         act.routes.size() == 2
+        act.corsOrigin == "*"
+        act.corsAllowedHeaders == "Content-Type"
         with(act.routes[0]) {
             id == "ethereum"
             blockchain == Chain.ETHEREUM

src/test/groovy/io/emeraldpay/dshackle/proxy/ProxyServerSpec.groovy

@@ -31,6 +31,7 @@ class ProxyServerSpec extends Specification {
 
         then:
         1 * routes.post("/test", _)
+        1 * routes.options("/test", _)
         1 * routes.ws("/test", _)
     }
 

src/test/resources/dshackle-proxy-max.yaml

@@ -3,6 +3,8 @@ proxy:
   host: 0.0.0.0
   port: 8080
   preserve-batch-order: true
+  cors-origin: "*"
+  cors-allowed-headers: "Content-Type"
   routes:
     - id: ethereum
       blockchain: ethereum