add one minute chart + refactor rpc

- add one minute charts
- update disk io to use bytes
- update hub and agent connection interfaces / handlers to be more
flexible
- change agent cache to use cache time instead of session id
- refactor collection of metrics which require deltas to track
separately per cache time

internal/hub/ws/ws_test_helpers.go

@@ -0,0 +1,11 @@
+//go:build testing
+// +build testing
+
+package ws
+
+// GetPendingCount returns the number of pending requests (for monitoring)
+func (rm *RequestManager) GetPendingCount() int {
+	rm.RLock()
+	defer rm.RUnlock()
+	return len(rm.pendingReqs)
+}