Add support for bash/zsh completion

[yiannistri]

• Add support for bash and zsh completion
• Currently using the builtin cobra generated scripts but can be extended to support nouns

Fixes #1593

[hiddeco]

Except for the minor comment this looks good to me, thanks for putting time and effort into this 🌷

I would like another maintainer (maybe @stefanprodan or @squaremo) to have a look at this, as I am not really familiar with the ins and outs of Cobra.

[yiannistri]

@hiddeco seems like the docker container running kubeadm to set up the e2e tests run out of memory 😕Any idea if this is a transient failure and if so could we trigger the build again?

[hiddeco]

It is a transient error we are working on with the folks of Kind, I have rebased your PR to get rid of the commits from master that were accidentally pulled in, which has also triggered a new CI build 🤞

[hiddeco]

/additional-reviewer-roulette (whoever comes first)

[squaremo]

Do we want to distinguish syntactically between completion which is literal, and shell which is user input? (or indeed, give the possible values)

[hiddeco]

I think it would make sense here to utilize the shells (again), and put <> around the list to highlight the fact that they are options.

[yiannistri]

Good idea, only issue is that the Use field is also used by the root command as a way to distinguish which of the commands need to skip port forward. So the completion command would have to get instantiated there (or come up with a different way of detecting which commands are run). Alternatively, we could change it to completion SHELL to distinguish them, similar to kubectl. What do you think?

[hiddeco]

Given people are hopefully already familiar with kubectl, I think that’s a good alternative.

[squaremo]

Solid work, thank you!

[squaremo]

(needs a rebase before it can be merged; if you don't get to it @yiannistri then someone will do it eventually :-)

[hiddeco]

@yiannistri can you please rebase on top of master (and maybe smash your commits together)?

[hiddeco]

Thank you @yiannistri! 🌻