[ci] Add new example chart meant for testing and QA

[mallardduck]

Issue: #98

In order to expand the testing done to this project before PRs are merged I've added a very basic E2E testing suite (based on PromFed project's tooling). This along with the other CI tooling has us covered for the most basic of tests. These are:

• Ensuring the expected binary Arch's for binaries in the image
• Verifying that the images build can be deployed (in general)

Any more specific testing (replicating chart upgrade jobs/etc) should be implemented later in a follow up effort. This is because that style of testing is most relevant to the charts using this image for that action and those charts are the ones that define the job/deployment. The only requirement of this image for that is that the image exists and has the kuberlr and kubectl binaries.

In other words, the e2e scripts should be expanded to cover executing those test-cases based on what makes sense. This is not easy to accomplish with a single chart, so that's why it was excluded from this PR effort. They however would fit better as one-off deployments (outside of helm) as static manifests and then verifying those had expected results.

Backports

This should be backported to the current release branches too.

---

This is a cleaned up version of: #91

[mallardduck]

/backport release/v4.x

[github-actions]

Not creating port PR, there was an error running git am -3:

Applying: Add new kubectl-test chart for helping validate images
Applying: Add readme to testing chart
Applying: Add support for kuberlrAllowDownload in the test chart
Applying: support build scripts
Applying: Add release step for debug helm chart creation
Applying: Adjust global config example
Applying: make examples more consistent
Applying: Fix duplicate targets
Applying: Fix ci cleanup step before package-ci
Applying: Add bash assertion helpers - for later use to test the images - and use it for CI scripts too
Applying: initial e2e script setup
.git/rebase-apply/patch:174: trailing whitespace.
      - 
.git/rebase-apply/patch:178: trailing whitespace.
      - 
.git/rebase-apply/patch:191: trailing whitespace.
      - 
.git/rebase-apply/patch:252: trailing whitespace.
    if [[ -n ${RANCHER_CLUSTER} && ${RANCHER_CLUSTER} != "local" ]]; then 
.git/rebase-apply/patch:256: trailing whitespace.
    fi 
warning: 5 lines add whitespace errors.
Using index info to reconstruct a base tree...
M	.gitignore
Falling back to patching base and 3-way merge...
Auto-merging .gitignore
CONFLICT (content): Merge conflict in .gitignore
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
Patch failed at 0011 initial e2e script setup