add systemd-resolved configuration feature

[g0rgamesh]

No description provided.

[gemini-code-assist]

Code Review

This pull request refactors the systemd-resolved configuration by introducing a block that conditionally enables the service, creates a configuration directory, deploys a DNS configuration template, and restarts the service. Feedback on these changes includes ensuring idempotency by conditionally restarting systemd-resolved only when the template configuration changes (and using the FQCN for the template module), as well as guarding the resolv_nameservers variable in the template with an is defined check to prevent execution failures when the variable is not provided.

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