Support for functional operations

[kezike]

It would be great if we could enable support for functional operations on credential values.

This will enable template designers to transform a machine readable value to a human readable one. This came up for me when I wanted to use dates in the template. Because credential dates are often in ISO 8601 format (e.g., 2025-04-16T16:11:18.316Z), they are not readily suitable for human consumption (e.g., 4/16/2025 or 2025-04-16).

To solve this issue, I was tempted to use a jsonata function in a mustache template like this:

Date: {{$fromMillis($toMillis(validFrom), "[M]/[D]/[Y]")}}

...but since mustache is "logic-less", this is technically improper and not recognizable by common mustache libraries. So, we would either need to think of other templating languages that provide this type of support or provide a mechanism for this via a property in renderMethod.