Move current implementation into separate namespace

We will be moving ietf-hardware implementation from cla-sysrepo to
velia. Veliad daemon will manage not only the "system health" (the
current implementation) but it will also (in later commits) implement
ietf-hardware (RFC8348) [1] (report HW sensors readout to Sysrepo).

This commit prepares the directory structure (i.e., it moves the current
code into a namespace velia::health.
We will be adding new namespace velia::ietf_hardware throughout the next
few commits which will implement the support for ietf-hardware YANG
model.

[1] https://tools.ietf.org/html/rfc8348#appendix-A

Change-Id: I315c2575c5d50036d27cb0a11f5571ce9d615fe5
diff --git a/src/health/State.cpp b/src/health/State.cpp
new file mode 100644
index 0000000..4ccf108
--- /dev/null
+++ b/src/health/State.cpp
@@ -0,0 +1,23 @@
+#include "health/State.h"
+
+namespace velia::health {
+
+std::ostream& operator<<(std::ostream& os, State state)
+{
+    os << "State::";
+    switch (state) {
+    case State::ERROR:
+        os << "ERROR";
+        break;
+    case State::WARNING:
+        os << "WARNING";
+        break;
+    case State::OK:
+        os << "OK";
+        break;
+    }
+
+    return os;
+}
+
+}