feat: add a new type for the kubernetes hostname override mode

[tzneal]

Issue #, if available:

N/A

Description of changes:

Adds a new type to be used when configuring the hostname override mode.

[root@admin]# apiclient set settings.kubernetes.hostname-override-source=asd
Failed to change settings: Failed PATCH request to '/settings/keypair?tx=apiclient-set-0PV6YalhON4ZW9bb': Status 400 when PATCHing /settings/keypair?tx=apiclient-set-0PV6YalhON4ZW9bb: Unable to match your input to the data model.  We may not have enough type information.  Please try the --json input form.  Cause: Error during deserialization: unknown variant `asd`, expected `private-dns-name` or `instance-id` at line 1 column 47

[root@admin]# apiclient set settings.kubernetes.hostname-override-source=private-dns-name

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