fix: re-introduce k8s 1.18 CI testing

[clamoriniere]

What this PR does / why we need it:

Update our CI workflow configuration and add back CI chart testing with kubernetes v1.18.x. Since #1486 the CI job was failing on the chart testing with kubernetes v1.18. To keep our capability to merge PRs, we commented the testing for 1.18 in #1576.

After investigation we understood the issue: #1486 has pumped the kind-action from v1.5.0 to v1.10.0 which pumps the kind-action version from v0.17.0 to v0.22.0. However, kind v0.22.0 is not able anymore to start the node image v1.18.

To solve the issue we now express which kind version needs to be used with each kubernetes version. So we can reintroduce the charts testing on kubernetes cluster v1.18.

Which issue this PR fixes

(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged)

• fixes #

Special notes for your reviewer:

the draft PR https://github.com/DataDog/helm-charts/pull/1580 is here to test that with this change the chart validation is able to run test on 1.18 cluster

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• [x] Chart Version bumped
• [x] Documentation has been updated with helm-docs (run: .github/helm-docs.sh)
• [x] CHANGELOG.md has been updated
• [x] Variables are documented in the README.md
• [x] For Datadog Operator chart or value changes update the test baselines (run: make update-test-baselines)

[clamoriniere]

/merge

[dd-devflow[bot]]

:steam_locomotive: MergeQueue: pull request added to the queue

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[dd-devflow[bot]]

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This pull request was merged directly.