feat: store state of failed attestations

[jiparis]

Since we are discussing about storing the state of gated attestations, for consistency we could also store it in any other situation.

Initially, this would be like enforcing the remote state for all attestations, and then exposing it through the API. For any failed attestations, users would be able to see the status and debug potential issues in the attestation process.

For example, a workflow run describe for a failed attestation would clearly state the cause of the failure:

✗ chainloop wf run describe --id 093f2200-89d9-43fa-8c5d-6cd551f407cc
┌────────────────────────────────────────────────────────────────┐
│ Workflow                                                       │
├────────────────┬───────────────────────────────────────────────┤
│ ID             │ 9f05b10a-da13-4e69-b731-d24b319bf4c2          │
│ Name           │ gate-wf                                       │
│ Team           │                                               │
│ Project        │ gate-project                                  │
│ Version        │ v1.62.1+next (prerelease)                     │
├────────────────┼───────────────────────────────────────────────┤
│ Workflow Run   │                                               │
├────────────────┼───────────────────────────────────────────────┤
│ ID             │ 093f2200-89d9-43fa-8c5d-6cd551f407cc          │
│ Initialized At │ 16 Dec 25 07:22 UTC                           │
│ State          │ failed                                        │
│ Cause          │ mandatory materials not provided (my-material)│
│ Policy Status  │ N/A                                           │
│ Runner Link    │                                               │
└────────────────┴───────────────────────────────────────────────┘

[jiparis]

Closing with #2635