Werk #16152: host_config: bulk delete hosts requires at least 1 entry

This werk addresses an issue found by our QA team when bulk deleting hosts via the following endpoint.

/domain-types/host_config/actions/bulk-delete/invoke

The body for this endpoint requires that the entries fields is given a list of host names that the client wants to delete. However, when passing in an empty list, this was causing problems. To get around this, we've set a mininum value of items for the entries field to 1.

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