allow cache digest to pull in values from parameters

[bhearsum]

Tasks that are primarily created from action tasks often make use of action input as part of building task definitions, which ultimately impacts the outcome of a task. In circumstances like this, some parts of the action input (which ends up in parameters) needs to impact to the digest of cacheable tasks to ensure that tasks that are ultimately different do not share the same digest.

This is something we've needed and implemented for Firefox translations via a from-parameters section in the cache configuration.