Add artifact signature information to the generated index

[maxgio92]

What type of PR is this?

/kind feature

Any specific area of the project related to this PR?

/area registry
/area build

What this PR does / why we need it:

This PR is needed to provide required information for consumers in order to verify OCI signatures of rules officially distributed as OCI artifacts.

The registry.yaml index is consumed by current CI to generate the general Falco artifacts index https://github.com/falcosecurity/falcoctl/blob/gh-pages/index.yaml, which can be further consumed by falcoctl to verify artifacts (i.e. rules) signatures.

Which issue(s) this PR fixes:

Fixes #100

Special notes for your reviewer:

Only one signin implementation is currently supported, which is based on cosign. When signatures are generated by cosign in keyless mode, can provide the OIDC issuer and certificate identity (see falcosecurity/falcoctl#305).

Furthermore, this PR adds black box and white box unit tests.

The same feature should be applied to the registry tool of the plugins (falcosecurity/plugins#312).

[maxgio92]

I'd wait for #64 to merge this.
/hold

[incertum]

@maxgio92 could we get a rebase? Thanks. Is this ready to be reviewed and merged?
CC @LucaGuerra

[LucaGuerra]

I've identified and fixed a bug in falcoctl that prevented this info from being parsed correctly. Just want to make sure that all is good before merging this one because it'll affect Falco 0.36.0 users :) My plan is to finish this work within a week.

[maxgio92]

Hey @incertum @LucaGuerra, I've just rebased on top of main and with the occasion I upgraded falcoctl dependency to v0.6.1

[LucaGuerra]

Thank you for the update and rebase! I have tested this with the current registries and indexes and it works as we expect 🎉

Now, after the Go update in test-infra is complete we'll be able to deploy this.

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: LucaGuerra, maxgio92

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• OWNERS [LucaGuerra]

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[incertum]

/unhold