Add basic E2 agent through git submodule

- Add E2 agent that leverages FlexRIC e2ap library
- Add documentation in openair2/E2AP/README.md
- Currently, statistics exported are random

openair2/E2AP/RAN_FUNCTION/O-RAN/ran_func_kpm.h

@@ -0,0 +1,13 @@
+#ifndef RAN_FUNC_SM_KPM_READ_WRITE_AGENT_H
+#define RAN_FUNC_SM_KPM_READ_WRITE_AGENT_H
+
+#include "../../flexric/src/agent/e2_agent_api.h"
+
+void read_kpm_sm(void*);
+
+void read_kpm_setup_sm(void*);
+
+sm_ag_if_ans_t write_ctrl_kpm_sm(void const* src);
+
+#endif
+