expiration date might prevent installation

[lukpueh]

[based on the X41 specification and source code audit]

The expiration date in the layout files might prevent users from properly verifying and installing a product after that date. This might force the users of in-toto to create additional releases that offer no functional changes or use overly long expiration dates.

Solution Advice
X41 recommends to add an option to enforce a certain version counter value.

[lukpueh]

existing solution: ITE-2

[lukpueh]

Also note that issuing a new layout for a supply chain does not necessarily require creating a new release of the product.

[adityasaky]

Does the use of ITE-2 to associate layouts generally handle this? Can we close it with #75 even if expiration isn't explicitly mentioned there?