feat(core): Default encoding/decoding limits (#1335)

* feat(core): Default encoding/decoding limits

This PR adds new defaults for both client and server max
encoding/decoding message size limits. By default, the max message
decoding size is `4MB` and the max message encoding size is
`usize::MAX`.

This is follow up work from https://github.com/hyperium/tonic/pull/1274

BREAKING: Default max message encoding/decoding limits

* update generated code

tests/integration_tests/proto/test.proto

@@ -8,3 +8,14 @@ service Test {
 
 message Input {}
 message Output {}
+
+service Test1 {
+  rpc UnaryCall(Input1) returns (Output1);
+}
+
+message Input1 {
+  bytes buf = 1;
+}
+message Output1 {
+  bytes buf = 1;
+}