chore(kms): add delete-at field

[luxium30]

Description

This PR adds the delete-at field for KMS keys. The convention is printing out every field, even when unset.

go run main.go kms key show 019e9327-0059-702f-b211-e2e0217f982c --zone de-fra-1

┼─────────────────┼────────────────────────────────────────────────────┼
│     KMS KEY     │                                                    │
┼─────────────────┼────────────────────────────────────────────────────┼
│ ID              │ 019e9327-0059-702f-b211-e2e0217f982c               │
│ Name            │ serf                                               │
│ Created At      │ 2026-06-04 15:01:07.289146061 +0000 UTC            │
│ Multizone       │ false                                              │
│ Origin Zone     │ de-fra-1                                           │
│ Status          │ enabled                                            │
│ Replicas Status │ -                                                  │
│ Material        │ auto: false                                        │
│                 │ createdAt: 2026-06-04 15:01:07.289146061 +0000 UTC │
│                 │ version: 1                                         │
│ Rotation        │ auto: true                                         │
│                 │ count: 0                                           │
│                 │ nextAt: 2027-06-04 15:01:07.292841723 +0000 UTC    │
│                 │ rotationPeriod: 365                                │
│ Usage           │ encrypt-decrypt                                    │
│ Source          │ exoscale-kms                                       │
│ Description     │ sdfsef                                             │
│ Delete At       │ n/a                                                │
┼─────────────────┼────────────────────────────────────────────────────┼

go run main.go kms key show 019ef4a7-c5d9-7880-8a78-4ebfaacb4423

┼─────────────────┼────────────────────────────────────────────────────┼
│     KMS KEY     │                                                    │
┼─────────────────┼────────────────────────────────────────────────────┼
│ ID              │ 019ef4a7-c5d9-7880-8a78-4ebfaacb4423               │
│ Name            │ aab                                                │
│ Created At      │ 2026-06-23 13:26:15.647876511 +0000 UTC            │
│ Multizone       │ false                                              │
│ Origin Zone     │ ch-gva-2                                           │
│ Status          │ pending-deletion                                   │
│ Replicas Status │ -                                                  │
│ Material        │ auto: false                                        │
│                 │ createdAt: 2026-06-23 13:26:15.647876511 +0000 UTC │
│                 │ version: 2                                         │
│ Rotation        │ auto: true                                         │
│                 │ count: 1                                           │
│                 │ nextAt: 2027-06-23 13:24:56.41204593 +0000 UTC     │
│                 │ rotationPeriod: 365                                │
│ Usage           │ encrypt-decrypt                                    │
│ Source          │ exoscale-kms                                       │
│ Description     │                                                    │
│ Delete At       │ 2026-07-22 09:51:26.813122066 +0000 UTC            │
┼─────────────────┼────────────────────────────────────────────────────┼

Checklist

(For exoscale contributors)

• Changelog updated (under Unreleased block, and add the Pull Request #number for each bit you add to the CHANGELOG.md)
• Testing

Testing

[jbelo]

We should understand the effect of removing a time.Time field, when it is zero, from all output.