zh: simplify gcp/gke deployment guide (pingcap#672)

* gke

* simplify gcp/gke deployment guide

* Update zh/deploy-on-gcp-gke.md

Co-authored-by: DanielZhangQD <[email protected]>

* Update zh/deploy-on-gcp-gke.md

Co-authored-by: DanielZhangQD <[email protected]>

* add node selector for tiflash and ticdc

* Apply suggestions from code review

Co-authored-by: Ran <[email protected]>

* address comments

* Apply suggestions from code review

Co-authored-by: DanielZhangQD <[email protected]>

* Update zh/deploy-on-gcp-gke.md

Co-authored-by: Ran <[email protected]>

* Apply suggestions from code review

Co-authored-by: Ran <[email protected]>

Co-authored-by: DanielZhangQD <[email protected]>
Co-authored-by: Ran <[email protected]>
Co-authored-by: ti-srebot <[email protected]>