GitHub Actions cache build on main branch

[triffer]

Description
With our current config we create a cache with go dependencies for every PR. This caches can only be re-used in the same PR. That means the first workflows in a PR always have to download the dependencies, even when there are not changes to the dependencies.
To avoid that we can leverage the built-in usage of caches from the main branch.

Access restrictions provide cache isolation and security by creating a logical boundary between different branches or tags. Workflow runs can restore caches created in either the current branch or the default branch (usually main).

GitHub cache docs

Changes proposed in this pull request:

• Add main workflow with a step to run go build and create the cache

Related issue(s)