feat: don't switch zone for dns command

[mlec1]

Description

The DNS command are not zone dependent, so this MR remove the need to change the zone for DNS command.

The reason behind that: I created a role for DNS challenge for getting web certificate.

{
  "default-service-strategy": "deny",
  "services": {
    "dns": {
      "type": "rules",
      "rules": [
        {
          "expression": "parameters.has('type') && parameters.type != 'TXT'",
          "action": "deny"
        },
        {
          "expression": "parameters.has('name') && !parameters.name.startsWith('_acme-challenge')",
          "action": "deny"
        },
        {
          "expression": "resources.has('dns_domain_record') && resources.dns_domain_record.has('type') && resources.dns_domain_record.type != 'TXT'",
          "action": "deny"
        },
        {
          "expression": "resources.has('dns_domain_record') && resources.dns_domain_record.has('name') && !resources.dns_domain_record.name.startsWith('_acme-challenge')",
          "action": "deny"
        },
        {
          "expression": "operation in ['list-dns-domains', 'list-dns-domain-records', 'get-dns-domain-record', 'create-dns-domain-record', 'delete-dns-domain-record']",
          "action": "allow"
        }
      ]
    }
  }
}

I wanted to test if my role allows only the TXT records that I wanted. The easiest was to test with the exo cli.

However, due to the SwitchClientZoneV3, the role need also the permission compute.list-zones (or something similar), if I want to edit DNS Records with the exo cli, which is not needed for the tools like lego or cert-manager.

From what I understood, the client will be created within the buildClient. Let me know if I missed something.

Checklist

(For exoscale contributors)

• Changelog updated (under Unreleased block)
• Testing

Testing

Create, delete, update DNS records work.