Docs: Quickstart GKE Clean-Up

[danehans]

Update the quickstart guide with instructions for cleaning up the GKE Gateway installation.

[danehans]

@robscott @kfswain @ahg-g can someone from the Google docs team help with this issue? See 6a18beb for details.

[robscott]

@capri-xiyue are you able to help with this one?

[capri-xiyue]

@robscott You can assign it to me. I will do it when I have bandwidth. In addition, if something is GA blocker, please let me know so that I can keep track of it and make sure it get completed before our GA.

[capri-xiyue]

/assign

[danehans]

@capri-xiyue thanks for taking on this issue. GKE is the only remaining implementation missing cleanup steps. Do you have an ETA for your PR to fix this issue?

[capri-xiyue]

@danehans I will send a PR by the end of this week. Does that work for you?

[capri-xiyue]

#1064 sent