Add common action items for the new predicate vetting process

[marcelamelara]

This PR explicitly adds three main common action items that are part of the vetting process for new predicate types:

• updating the list of existing predicates
• adding a proto definition to generate language bindings
• updating the URL redirects for predicateType URIs that are defined within the in-toto.io/attestation namespace

fixes #313

[pxp928]

LGTM

[adityasaky]

Possibly out of scope for this PR but can this guide be updated to include inline ITE-9 recommendations so we don't turn ITE-9 into a living doc?

[marcelamelara]

Possibly out of scope for this PR but can this guide be updated to include inline ITE-9 recommendations so we don't turn ITE-9 into a living doc?

Hmm, it may be within scope. Do you have a specific list of recommendations that we can already add?

[adityasaky]

1. Open a PR following [ITE-9] formatting guidelines.

Probably just inlining this so the ITE-9 reference is just for where it came from. Any future formatting updates then don't need to happen in ITE-9.

[marcelamelara]

Probably just inlining this so the ITE-9 reference is just for where it came from. Any future formatting updates then don't need to happen in ITE-9.

@adityasaky we figured that ITE-9 is the authoritative source for predicate spec formatting, are you suggesting that any future format updates should be specified here instead?

[adityasaky]

@adityasaky we figured that ITE-9 is the authoritative source for predicate spec formatting, are you suggesting that any future format updates should be specified here instead?

yes. That'd enable ITE-9 to be accepted and then move into "final" status, for example (https://github.com/in-toto/ITE/blob/master/ITE/1/README.adoc#ite-workflow). My understanding of the ITE process is that they're not intended to be living documents, even if changes are expected to be far and few in between.

So re-specifying the format in the attestation docs + stating they originated from ITE-9 is probably fine?

[marcelamelara]

My understanding of the ITE process is that they're not intended to be living documents, even if changes are expected to be far and few in between.

So re-specifying the format in the attestation docs + stating they originated from ITE-9 is probably fine?

Thanks for the clarification. Now this makes sense. My take is to handle this in a dedicated PR, though.

[marcelamelara]

@pxp928 @TomHennen Given the discussion with @adityasaky , are you with merging this PR as-is now?

[adityasaky]

Thanks for the clarification. Now this makes sense. My take is to handle this in a dedicated PR, though.

Sounds good to me!