Add Docker-based GitHub Actions Workflows

[atc0005]

CHANGES

Add GitHub Actions which use containers created and managed through the atc0005/go-ci project.

This results in three workflows:

• New, primary workflow

  • with parallel linting, testing and building tasks
  • with three Go environments
  • "old stable"
  • "stable"
  • "unstable"
    • this will be replaced with the next alpha, beta, rc release of Go and other linting tools that are not tested well enough to be considered "stable"
  • Makefile is not used in this workflow
  • staticcheck linting using latest stable version provided by the atc0005/go-ci containers

• Separate Makefile-based linting and building workflow

  • intended to help ensure that local Makefile-based builds that are referenced in project README files continue to work as advertised until a better local tool can be discovered/explored further
  • use golang:latest container to allow for Makefile-based linting tooling installation testing since the atc0005/go-ci project provides containers with those tools already pre-installed
  • linting tasks use container-provided golangci-lint config file except for the Makefile-driven linting task which continues to use the repo-provided copy of the golangci-lint configuration file

• Add Quick Validation workflow

  • run on every push, everything else on pull request updates
  • linting via golangci-lint only
  • testing
  • no builds

Other changes:

• Makefile lintinstall recipe installs the very latest stable version of the golangci-lint binary instead of locking a specific version
  • this should reduce dependency "gardening"

REFERENCES

• fixes GH-21
• refs atc0005/todo#22
• see also the https://github.com/atc0005/go-ci project