fix: add missing CRD link to helm chart readme

Motivation

The helm chart's README.md was missing instructions to update / apply the ClickhouseKeeperInstallation CRD.

Modifications

Add kubectl apply ... command for the CHK CRD to chart description
Add README.md.gotmpl (see note below)
Update README.md via helm-docs
Remove helm-docs minimum version comment in ./dev/generate_helm_chart.sh since it is no longer needed

Note on `README.go.tmpl`

This PR also includes a new file: README.md.gotmpl

The reason this file is being included is because it allows for strict control over what is included in the final README.md. The contents of this file are copy-pasted from the helm-docs defaults (you can find them below the table here), except for the last template section:

{{ template "helm-docs.versionFooter" . }}

This part has been omitted in order to preserve the current README.md format.

The same functionality can be achieved by using the --skip-version-footer flag when calling helm-docs. I had originally included this in dev/generate_helm_chart.sh as part of (#1555); however, it was subsequently removed in https://github.com/Altinity/clickhouse-operator/commit/3ae32ee2b8c813265d578d4442aadfa30085200c by @sunsingerus.

Hopefully this approach is more suitable.

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Altinity / clickhouse-operator