add option to enable compression for gRPC-server (#133)

* add grpc server compression

* change compression config defaults

* fix review issue

* add note about compression in readme

* add compression section to server config doc

docs/03-server-config.adoc

@@ -21,6 +21,12 @@ tls:
   client:
     require: true
     ca: "ca.crt"
+
+compression:
+  grpc:
+    server:
+      enabled: false
+
 cluster:
   include: "upstreams.yaml"
 ----
@@ -29,6 +35,7 @@ It configures following:
 
 - server is listening with gRCP API on `0.0.0.0:2449`
 - TLS is enabled
+- compression is disabled for gRPC server (enabled by default)
 - server certificate is located at `server.crt` with the key for it at `server.p8.key`
 - the server requires a client authentication by TLS client certificate signed by `ca.crt` certificate
 - no JSON RPC is configured
@@ -51,6 +58,10 @@ a| `tls`
 | TLS configuration for gRPC.
 See link:08-authentication.adoc[Authentication] for details
 
+a| `compression`
+|
+| Compression configuration
+
 a| `proxy`
 |
 | Proxy configuration
@@ -60,6 +71,21 @@ a| `upstreams`
 | Upstreams configuration
 |===
 
+=== Compression
+Compression is enabled by default on the gRPC server
+(the server accepts compressed requests and can send compressed responses).
+Responses will be compressed if a client supports compression (sends relevant headers),
+otherwise, communication will be uncompressed.
+But if for some reason you need to disable compression forcibly,
+add the lines below to the config:
+[source,yaml]
+----
+compression:
+  grpc:
+    client:
+      enabled: false
+----
+
 === Enabling JSON RPC proxy
 
 In addition to the gRPC protocol, Dshackle provides access compatible with Bitcoin and Ethereum JSON RPC.