feat: create a variable for node exporter command

[dudy-duce]

Users can override this list to customize collectors.

Why this approach

• Keeping the command as a list of strings matches how the template renders the JSON command array.
• Using to_json ensures any characters (like backslashes or parentheses) are properly escaped in JSON.
• Defaulting the variable to the current options preserves existing behavior and provides an easy override point.

Edge cases considered

• If a user overrides the variable with a single string or wrongly typed value — best practice is to override as a YAML list of strings (examples below). The template assumes a list; providing any other type may render incorrectly.
• The TLS flag still prepends the --web.config.file entry when tls_cert_exists is true, so that behavior is unchanged.

Resolve issue.

[openshift-ci]

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[openshift-ci]

Hi @dudy-duce. Thanks for your PR.

I'm waiting for a github.com member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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