[#24] Client: Implement pool part1

first iteration - base classes and methods

Signed-off-by: Pavel Gross <p.gross@yadro.com>

src/FrostFS.SDK.ClientV2/Poll/HealthyStatus.cs

@@ -0,0 +1,18 @@
+namespace FrostFS.SDK.ClientV2;
+
+// values for healthy status of clientStatusMonitor.
+public enum HealthyStatus
+{
+    // statusUnhealthyOnDial is set when dialing to the endpoint is failed,
+    // so there is no connection to the endpoint, and pool should not close it
+    // before re-establishing connection once again.
+    UnhealthyOnDial,
+
+    // statusUnhealthyOnRequest is set when communication after dialing to the
+    // endpoint is failed due to immediate or accumulated errors, connection is
+    // available and pool should close it before re-establishing connection once again.
+    UnhealthyOnRequest,
+
+    // statusHealthy is set when connection is ready to be used by the pool.
+    Healthy
+}