Add make targets for applying and checking style

Need to change to the project's top srcdir, as citus_indent expects to
be able to find styled files using git ls-files, and VPATH builds would
otherwise not return any results.

Makefile

@@ -42,6 +42,13 @@ clean-csql:
 install: install-csql
 clean: clean-csql
 
+# apply or check style
+reindent:
+	cd ${citusdb_abs_top_srcdir} && citus_indent --quiet
+check-style:
+	cd ${citusdb_abs_top_srcdir} && citus_indent --quiet --check
+.PHONY: reindent check-style
+
 # depend on install for now
 check: all install
 	$(MAKE) -C src/test/regress check-full