fix(contracts): Store and show correct description for workflow contracts

[jiparis]

With the introduction of contracts schema V2, the description field now resides in the raw metadata section in the contract header. This PR makes the API and CLI show the description from the right revision.

Example: two revisions of the same contract, with different descriptions

✗ chainloop workflow contract describe --name test-create --revision 2
INF To download the contract, run the command with the "--output schema" option
┌─────────────────────────────────────────────────────────────┐
│ Contract                                                    │
├──────────────────────┬──────────────────────────────────────┤
│ Name                 │ test-create                          │
├──────────────────────┼──────────────────────────────────────┤
│ Scope                │ project/test-create                  │
├──────────────────────┼──────────────────────────────────────┤
│ Description          │ Another description for the contract │
├──────────────────────┼──────────────────────────────────────┤
│ Associated Workflows │                                      │
├──────────────────────┼──────────────────────────────────────┤
│ Revision number      │ 2                                    │
├──────────────────────┼──────────────────────────────────────┤
│ Revision Created At  │ 19 Nov 25 10:17 UTC                  │
└──────────────────────┴──────────────────────────────────────┘
┌─────────────────────────────────────────────────────┐
│ apiVersion: chainloop.dev/v1                        │
│ kind: Contract                                      │
│ metadata:                                           │
│   name: test-create                                 │
│   description: Another description for the contract │
│ spec:                                               │
│   materials:                                        │
│     - name: hello-material                          │
│       type: ARTIFACT                                │
│   runner:                                           │
│     type: GITHUB_ACTION                             │
└─────────────────────────────────────────────────────┘
➜  cldev workflow contract describe --name test-create --revision 1
INF To download the contract, run the command with the "--output schema" option
┌────────────────────────────────────────────────────────┐
│ Contract                                               │
├──────────────────────┬─────────────────────────────────┤
│ Name                 │ test-create                     │
├──────────────────────┼─────────────────────────────────┤
│ Scope                │ project/test-create             │
├──────────────────────┼─────────────────────────────────┤
│ Description          │ Description of default contract │
├──────────────────────┼─────────────────────────────────┤
│ Associated Workflows │                                 │
├──────────────────────┼─────────────────────────────────┤
│ Revision number      │ 1                               │
├──────────────────────┼─────────────────────────────────┤
│ Revision Created At  │ 19 Nov 25 10:07 UTC             │
└──────────────────────┴─────────────────────────────────┘
┌────────────────────────────────────────────────┐
│ apiVersion: chainloop.dev/v1                   │
│ kind: Contract                                 │
│ metadata:                                      │
│   name: test-create                            │
│   description: Description of default contract │
│ spec:                                          │
│   runner:                                      │
│     type: GITHUB_ACTION                        │
└────────────────────────────────────────────────┘