feat(vm, lxc): add new initialization.dns.servers param to vm and container

[rafsaf]

Contributor's Note

• I have added / updated documentation in /docs for any user-facing features or additions.
• I have added / updated templates in /example for any new or updated resources / data sources.
• I have ran make example to verify that the change works as expected.

Proof of Work

Added servers param, deprecate old server param. Apply AFAIK works as expected, tried some of combinations:

• old server and no servers
• both server and servers
• new servers without server
• old server and no servers -> apply -> then only servers

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Closes #816

[bpg]

Thank you so much for adding this, @rafsaf!

LGTM! 🚀