feat(CLI): implement method for querying stakes

 Please enter the commit message for your changes. Lines starting

src/cli/node/json_rpc_client.rs

@@ -41,7 +41,9 @@ use witnet_data_structures::{
 };
 use witnet_node::actors::{
     chain_manager::run_dr_locally,
-    json_rpc::api::{AddrType, GetBlockChainParams, GetTransactionOutput, PeersResult},
+    json_rpc::api::{
+        AddrType, GetBlockChainParams, GetTransactionOutput, PeersResult, QueryStakesArgument,
+    },
     messages::{
         AuthorizeStake, BuildDrt, BuildStakeParams, BuildStakeResponse, BuildVtt, GetBalanceTarget,
         GetReputationResult, MagicEither, SignalingInfo, StakeAuthorization,
@@ -1826,6 +1828,34 @@ pub fn priority(addr: SocketAddr, json: bool) -> Result<(), failure::Error> {
     Ok(())
 }
 
+pub fn query_stakes(
+    addr: SocketAddr,
+    validator: Option<String>,
+    withdrawer: Option<String>,
+) -> Result<(), failure::Error> {
+    let mut stream = start_client(addr)?;
+
+    let params = match (validator, withdrawer) {
+        (Some(validator), Some(withdrawer)) => {
+            Some(QueryStakesArgument::Key((validator, withdrawer)))
+        }
+        (Some(validator), _) => Some(QueryStakesArgument::Validator(validator)),
+        (_, Some(withdrawer)) => Some(QueryStakesArgument::Withdrawer(withdrawer)),
+        (None, None) => None,
+    };
+
+    let response = send_request(
+        &mut stream,
+        &format!(
+            r#"{{"jsonrpc": "2.0","method": "queryStakes", "params": {}, "id": 1}}"#,
+            serde_json::to_string(&params).unwrap()
+        ),
+    )?;
+    log::info!("{}", response);
+
+    Ok(())
+}
+
 #[derive(Serialize, Deserialize)]
 struct SignatureWithData {
     address: String,

src/cli/node/with_node.rs

@@ -290,6 +290,11 @@ pub fn exec_cmd(
         Command::AuthorizeStake { node, withdrawer } => {
             rpc::authorize_st(node.unwrap_or(default_jsonrpc), withdrawer)
         }
+        Command::QueryStakes {
+            node,
+            withdrawer,
+            validator,
+        } => rpc::query_stakes(node.unwrap_or(default_jsonrpc), withdrawer, validator),
     }
 }
 
@@ -785,6 +790,15 @@ pub enum Command {
         #[structopt(long = "withdrawer")]
         withdrawer: Option<String>,
     },
+    QueryStakes {
+        /// Socket address of the Witnet node to query
+        #[structopt(short = "n", long = "node")]
+        node: Option<SocketAddr>,
+        #[structopt(short = "v", long = "validator")]
+        validator: Option<String>,
+        #[structopt(short = "w", long = "withdrawer")]
+        withdrawer: Option<String>,
+    },
 }
 
 #[derive(Debug, StructOpt)]