Apply go module caching and build caching to Prow jobs

Istio Prow had some work on enabling go module cache and build cache, and got pretty good improvement on reducing the job running time, see the comments and descriptions in https://github.com/istio/test-infra/pulls?q=is%3Apr+cache.

Since it has been reported by some contributors that Prow is significantly slower than GitHub actions in build images, we should try if the same trick can be used to improve the performance of running Prow jobs for Knative.

/kind enhancement

Start by reviewing the linked Istio test-infra pull requests and their descriptions for the Go module and build cache approach. Then locate how Knative Prow jobs build images and run Go work, and compare job performance before and after caching. Done means demonstrating a measurable improvement in Prow job runtime with the relevant jobs still passing.

Written by the indexing model from the issue text.