`ci` workflow not used by provider-kubernetes - need support for e2e integration?

I noticed provider-kubernetes does not use the reusable ci workflow

I think we should change it to use the reusable workflow, otherwise we'll have to manage action versions in two repos.

I'm not sure why it's not used, I suspect it's because of the lack of e2e support in this repo

## Suggested fix

Add an optional input `e2e-command` (which in this case could be `make e2e`
Add conditions to only run when e2e-command is defined

Start by comparing provider-kubernetes's workflow usage with the reusable ci workflow and inspect how inputs are declared and consumed. Verify that an optional e2e-command can run make e2e only when defined, while the existing workflow continues to work without it.

Written by the indexing model from the issue text.