Update documentation sections about ethereum PoS connection (#150)

docs/04-upstream-config.adoc

@@ -73,7 +73,8 @@ cluster:
       options:
         disable-validation: true
       connection:
-        ethereum:
+        ethereum-pos:
+            execution:
               rpc:
                 url: "https://mainnet.infura.io/v3/${INFURA_USER}"
                 basic-auth:

docs/reference-configuration.adoc

@@ -110,7 +110,8 @@ cluster:
         disabled:
           - name: "admin_shutdown"
       connection:
-        ethereum:
+        ethereum-pos:
+            execution:
               rpc:
                 url: "http://localhost:8545"
               ws:
@@ -124,7 +125,8 @@ cluster:
       options:
         disable-validation: true
       connection:
-        ethereum:
+        ethereum-pos:
+            execution:
               rpc:
                 url: "https://mainnet.infura.io/v3/fa28c968191849c1aff541ad1d8511f2"
                 basic-auth:
@@ -608,7 +610,8 @@ cluster:
     - id: local
       chain: ethereum
       connection:
-        ethereum:
+        ethereum-pos:
+            execution:
               rpc:
                 url: "http://localhost:8545"
               ws:
@@ -654,7 +657,8 @@ configuration, and may be omitted for most of the situations.
     disabled:
       - name: "admin_shutdown"
   connection:
-    ethereum:
+    ethereum-pos:
+      execution:
           rpc:
             url: "http://localhost:8545"
           ws:
@@ -718,9 +722,9 @@ See link:09-quorum-and-selectors.adoc[Quorum and Selectors]
 `not_empty` - accept not _null_ value, otherwise retry another upstream;
 `not_lagging` - accept response only from a fully synced upstream.
 
-| `connection.ethereum`
+| `connection.ethereum-pos`
 | yes
-| Connection configuration for Ethereum API
+| Connection configuration for Ethereum API of PoS network
 
 | `connection.bitcoin`
 | yes