Add shell completion support to RKE2

[caroline-suse-rancher]

Is your feature request related to a problem? Please describe.

Currently, RKE2 does not support shell completion.

Describe the solution you'd like

Enable shell completion on RKE2. Shell completion installation should also set up the correct environment variables for kubectl and crictl to work properly using the default RKE2 paths.

Additional context

Ideally, this may help address #5250 (Jira Ref: SURE-7427)

[megabreit]

In the original issue #5250 also ctr was mentioned, but the completion patch only deals with crictl. Is there any reason for that? Or was it just forgotten?

[brandond]

cc @vitorsavian - can we open another issue to track adding ctr?

[fmoral2]

validate on:
#6617 (comment)
#6459 (comment)
#6458 (comment)
#6457 (comment)

[megabreit]

Why didn't you just add a file to /etc/bash_completion.d like others do? This way things would work "automagically" and there would be no need to manually add it.

Why is rke2 completion bash not installing any completion?