exchanges/websocket: Implement subscription configuration (#1394)

* Websockets: Move Subscription to its own package

This allows the small type to be imported from both `config` and from
`stream` without an import cycle, so we don't have to repeat ourselves

* Subs: Renamed Currency to Pair

This was being mis-used through much of the code, and since we're
already touching everything, we might as well fix it

* Websockets: Add Subscription configuration

* Binance: Add subscription configuration

* Kucoin: Subscription configuration

* Simplify GenerateDefaultSubs
* Improve TestGenSubs coverage
* Test Candle Sub generation
* Support Candle intervals
* Full responsibility for formatting Channel name on GenerateDefaultSubs
  OR consumer of Subscribe
* Simplify generatePayloads as a result
* Fix test coverage of asset types in processMarketSnapshot

* Exchanges: Abstract ParallelChanOp

* Tests: Generic ws mock instances

* Kucoin: Fix intermittent conflict in test currs

Use isolated test instance for `TestGetOpenInterest`.

`TestGetOpenInterest` would occassionally change pairs before
GenerateDefault Subs.

gctrpc/buf.lock

@@ -4,10 +4,10 @@ deps:
   - remote: buf.build
     owner: googleapis
     repository: googleapis
-    commit: cc916c31859748a68fd229a3c8d7a2e8
-    digest: shake256:469b049d0eb04203d5272062636c078decefc96fec69739159c25d85349c50c34c7706918a8b216c5c27f76939df48452148cff8c5c3ae77fa6ba5c25c1b8bf8
+    commit: 28151c0d0a1641bf938a7672c500e01d
+    digest: shake256:49215edf8ef57f7863004539deff8834cfb2195113f0b890dd1f67815d9353e28e668019165b9d872395871eeafcbab3ccfdb2b5f11734d3cca95be9e8d139de
   - remote: buf.build
     owner: grpc-ecosystem
     repository: grpc-gateway
-    commit: a1ecdc58eccd49aa8bea2a7a9022dc27
-    digest: shake256:efdd86fbdc42e8b7259fe461a49656827a03fb7cba0b3b9eb622ca10654ec6beccb9a051229c1553ccd89ed3e95d69ad4d7c799f1da3f3f1bd447b7947a4893e
+    commit: 3f42134f4c564983838425bc43c7a65f
+    digest: shake256:3d11d4c0fe5e05fda0131afefbce233940e27f0c31c5d4e385686aea58ccd30f72053f61af432fa83f1fc11cda57f5f18ca3da26a29064f73c5a0d076bba8d92

gctrpc/rpc.proto

@@ -834,7 +834,7 @@ message WebsocketGetSubscriptionsRequest {
 
 message WebsocketSubscription {
   string channel = 1;
-  string currency = 2;
+  string pair = 2;
   string asset = 3;
   string params = 4;
 }

gctrpc/rpc.swagger.json

@@ -7580,7 +7580,7 @@
         "channel": {
           "type": "string"
         },
-        "currency": {
+        "pair": {
           "type": "string"
         },
         "asset": {