feat: attestation usability improvements

[migmartri]

I have a couple of usability suggestions that might be worth implementing

• If we are using the discovery mode, i.e do not provide kind, and ends up falling back to artifact kind, we should explain that it didn't fit any other material kind.

• If we pass explicitly a kind we should probably show the error message too, so instead of

  chainloop att add --value ~/Downloads/jira.cyclonedx.json --kind SBOM_CYCLONEDX_JSON
  ERR adding material: crafting material: invalid cyclonedx sbom file: unexpected material type

  it should show

  oesn't validate with http://cyclonedx.org/schema/bom-1.6.schema.json#                                
  [I#/components/0] [S#/properties/components/items/$ref] doesn't validate with '/definitions/component'                                 
  [I#/components/0/licenses] [S#/definitions/component/properties/licenses/$ref] doesn't validate with '/definitions/licenseChoice'    
    [I#/components/0/licenses] [S#/definitions/licenseChoice/oneOf] oneOf failed                                                       
      [I#/components/0/licenses/0] [S#/definitions/licenseChoice/oneOf/0/items/required] missing properties: 

• We should be able to provide a name so we do not need to use the autogenerated one. Tracked by: https://github.com/chainloop-dev/chainloop/issues/911

wdyt?

### Tasks
- [ ] explain discovery mode resolution when falling back
- [ ] output error when it's not part of autodiscovery
- [ ] https://github.com/chainloop-dev/chainloop/issues/911
- [ ] Document attestation modes https://github.com/chainloop-dev/chainloop/issues/901
- [ ] Look into accepting invalid artifacts

[javirln]

Regarding the last topic, here's the task for it with in depth explanation: https://github.com/chainloop-dev/chainloop/issues/911

[jiparis]

Thanks @migmartri. I'm afraid malformed documents are going to be a frequent issue. Given the fact that Chainloop's role is attesting, it might be reasonable to allow skipping the validation and still store it as a SBOM_CYCLONEDX_JSON, probably with an annotation validated=false. This way, Chainloop is attesting that the document exists but it's not validated so it cannot be fully trusted.

[anoncam]

Thanks @migmartri. I'm afraid malformed documents are going to be a frequent issue. Given the fact that Chainloop's role is attesting, it might be reasonable to allow skipping the validation and still store it as a SBOM_CYCLONEDX_JSON, probably with an annotation validated=false. This way, Chainloop is attesting that the document exists but it's not validated so it cannot be fully trusted.

Completely agree here. If a validation skip feature is implemented I think it should be explicit (user has to declare that is the desired outcome) and then that must be reflected in the metadata. My two cents.

[migmartri]

Thanks for the feedback. I agree with you both. What I am not sure about is if this feature should be either.

• a) skip validation or
• b) continue if validation error

I am leaning towards b since it can inform us whether the document was valid. If we skip the validation, we lose that info.

In other words, I'd implement something like att add --soft-validation to add the evidence regardless of the validation output. The result will contain two extra annotations

• valid: true|false
• soft-validation: true|false`

These two annotations would allow users for example to create a policy that enforces not to use this feature, meaning soft-validation can't be true.

Wdyt?