Initial commit with what I think we need

src/pg/sql/10_version.sql

@@ -0,0 +1,12 @@
+-- Version number of the extension release
+CREATE OR REPLACE FUNCTION cdb_observatory_version()
+RETURNS text AS $$
+  SELECT '@@VERSION@@'::text;
+$$ language 'sql' STABLE STRICT;
+
+-- Internal identifier of the installed extension instence
+-- e.g. 'dev' for current development version
+CREATE OR REPLACE FUNCTION _cdb_observatory_internal_version()
+RETURNS text AS $$
+  SELECT installed_version FROM pg_available_extensions where name='observatory' and pg_available_extensions IS NOT NULL;
+$$ language 'sql' STABLE STRICT;