Add protocol params to the api schema

- Problem here is that async api schema is not really suitable for
REST endpoints. The second problem is what to give as an example for protocol params?
Protocol parameters file is pretty big and I am not sure it brings value to the users
to see a big json output in the docs?

hydra-node/json-schemas/api.yaml

@@ -141,6 +141,22 @@ channels:
           type: request
           method: POST
           bindingVersion: '0.1.0'
+  /protocol-parameters:
+    description: Endpoint to obtain protocol parameters used in hydra-node.
+    servers:
+      - localhost-http
+    subscribe:
+      summary: Get cardano protocol parameters.
+      operationId: getProtocolParameters
+      description: |
+        Clients can request from hydra-node it's protocol parameters used on start.
+      message:
+        $ref: "api.yaml#/components/messages/ProtocolParameters"
+      bindings:
+        http:
+          type: response
+          method: GET
+          bindingVersion: '0.1.0'
 components:
   messages:
     ########
@@ -787,6 +803,58 @@ components:
       payload:
         $ref: "api.yaml#/components/schemas/TextEnvelopeTransaction"
 
+    ProtocolParameters:
+      title: ProtocolParameters
+      description: |
+         Cardano protocol parameters used in hydra-node.
+         Example used in hydra-cluster package: https://github.com/input-output-hk/hydra/blob/master/hydra-cluster/config/protocol-parameters.json .
+      payload:
+       type: object
+       example:
+         {
+             "collateralPercentage": 150,
+             "costModels": {
+                 "PlutusScriptV1": {},
+                 "PlutusScriptV2": {}
+             },
+             "decentralization": null,
+             "executionUnitPrices": {
+                 "priceMemory": 5.77e-2,
+                 "priceSteps": 7.21e-5
+             },
+             "extraPraosEntropy": null,
+             "maxBlockBodySize": 65536,
+             "maxBlockExecutionUnits": {
+                 "memory": 80000000,
+                 "steps": 40000000000
+             },
+             "maxBlockHeaderSize": 1100,
+             "maxCollateralInputs": 3,
+             "maxTxExecutionUnits": {
+                 "memory": 14000000,
+                 "steps": 10000000000
+             },
+             "maxTxSize": 16384,
+             "maxValueSize": 5000,
+             "minPoolCost": 0,
+             "minUTxOValue": null,
+             "monetaryExpansion": 1.78650067e-3,
+             "poolPledgeInfluence": 0.1,
+             "poolRetireMaxEpoch": 18,
+             "protocolVersion": {
+                 "major": 7,
+                 "minor": 0
+             },
+             "stakeAddressDeposit": 400000,
+             "stakePoolDeposit": 500000000,
+             "stakePoolTargetNum": 50,
+             "treasuryCut": 0.1,
+             "txFeeFixed": 0,
+             "txFeePerByte": 0,
+             "utxoCostPerWord": 34488,
+             "utxoCostPerByte": 4310
+         }
+
   ########
   #
   # Schemas