[Bug]: Should Archivista use DSSE envelope signature keyid as optional?

[kairoaraujo]

What steps did you take and what happened:

As reported by Adam Nauth in our Slack channel

Using sigstore to sign some metadata - a key ID isn't part of the resulting data. https://github.com/sigstore/sigstore/blob/main/pkg/signature/dsse/dsse.go#L65
This means Archivista cannot handle it on upload - getting a key id length error when it's blank. Note: The DSSE allows key id to be blank.
Is there an alternative way to upload data without a key id?

What did you expect to happen:

Should the Archivista make key id optional while storing, see below some code track.

Anything else you would like to add:

sigstore dsse envelope signature from go-sslib
https://github.com/secure-systems-lab/go-securesystemslib/blob/69233cc2977ebd65aef18b14e4ee26fe090c5146/dsse/envelope.go#L35

archivista dsse envelope signature from go-witness
https://github.com/in-toto/go-witness/blob/1cf974d08dd9d3bf039644970cf02652916d0cd8/dsse/dsse.go#L73

We parse it and use key_id as NotEmpty

archivista/ent/schema/signature.go

Line 35 in cf77c3b

field.String("key_id").NotEmpty(),