docs: fix stale import documentation link

[imansadegh]

Motivation

Fixes #2759. The [imported] link in the vsphere_virtual_machine resource docs pointed at /docs/import/index.html, a relative path from the old terraform.io docs site that no longer resolves correctly.

While fixing it I found the same stale link in four other resource docs (vnic, host_port_group, host, datacenter) that hadn't been updated when the rest of the docs moved to https://developer.hashicorp.com/terraform/cli/import -- fixed those too so the whole repo is consistent.

Documentation-only change, no code touched.

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[tenthirtyam]

#2759 is already assigned to me. We can accept this change however you'll need to sign the CLA.

Marking as draft.

Ryan

[tenthirtyam]

We can accept this change however you'll need to sign the CLA.