docs: use single tags option for the controlplane nodes

[roivanov]

Pull Request

What? (description)

Seeing the following error:

talosctl --talosconfig talosconfig bootstrap

error executing bootstrap: rpc error: code = Unavailable desc = connection error: desc = "transport: Error while dialing: dial tcp 34.111.111.111:50000: i/o timeout"

The reason is that gcloud compute instances create command only takes tags as a comma-separated list. Otherwise, only the last one is applied

From the command help:

--tags=TAG,[TAG,...]
        Specifies a list of tags to apply to the instance. These tags allow
        network firewall rules and routes to be applied to specified VM
        instances. See gcloud compute firewall-rules create(1) for more
        details.

Why? (reasoning)

Acceptance

Please use the following checklist:

• [ ] you linked an issue (if applicable)
• [ ] you included tests (if applicable)
• [ ] you ran conformance (make conformance)
• [ ] you formatted your code (make fmt)
• [ ] you linted your code (make lint)
• [ ] you generated documentation (make docs)
• [ ] you ran unit-tests (make unit-tests)

See make help for a description of the available targets.

[frezbo]

/m