chore(Makefile): pin dependencies

[weisdd]

• Makefile:
  • moved toolchain installation to Toolchain.mk:
    • to declutter Makefile;
    • to make it possible to calculate hash against the file, so we can later introduce proper binary caching;
  • pinned the existing versions except for:
    • setup-envtest:
      • we've been relying on latest version, I pinned it to v0.20.4;
    • crdoc:
      • bumped version from a commit hash to the latest tag to make binary name more predictable;
    • kustomize:
      • bumped version to v5.6.0, so native darwin/arm64 build is used (previously, it would fall back to darwin/amd64);
  • binary names now include version suffix, so the tools will be transparently upgraded should we bump any of the versions;
  • chainsaw, controller-gen, setup-envtest are now downloaded as binaries instead of relying on go install to speed up the installation process;
  • renamed some of the targets to make them appear in help target (changed separator from / -> -);
  • workflows:
    • moved kustomize overlay validation from pr-validation workflow to Makefile, it's now part of test target;
    • moved kustomize steps that set release image and generate GitHub assets from release workflow to Makefile, so kustomize can be pinned there;
    • moved helm template/lint step from pr-validation workflow to Makefile, it's now part of test target;
    • removed calls to install unused binaries for ko and chainsaw from e2e workflow.

There are plenty of things that can be further improved in Makefile, it should just be a good start.

[weisdd]

(finished with my experiments for now, so the PR should be OK to review)

[Baarsgaard]

I really like the approach of a dedicated Toolchain makefile and simpler Action workflows!

[Baarsgaard]

Aside from the last comment below I think this looks good as is!