implement k8s service discovery (#988)

* implement k8s service discovery

* simplify code

* use default namespace if not provided

* disable codecov bot comment

* ignore adhoc dir

* simplify building target in NewClient

* reformat code

* Fix filepath (#990)

* format code, and reorg imports (#991)

* add more unit test

Co-authored-by: anqiansong <anqiansong@gmail.com>

.codecov.yml

@@ -1,4 +1,5 @@
+comment: false
 ignore:
   - "doc"
   - "example"
-  - "tools"
+  - "tools"