Migrating all cert-manager sub-projects to "Makefile modules"

[inteon]

We want to reduce the time spent on "dumb" tasks (upgrading dependencies, fixing small bugs, ...).

1. A first improvement we made was enabling dependabot grouped upgrades, which allows us to more easily upgrade Go dependencies.
2. The second improvement we envision is to deduplicate most of our Makefile logic across projects and centralise the logic in a single location. This will prevent Makefile improvements & fixes to be applied to only a single project and thus should help us use the best quality and most feature-complete logic in every project. Additionally, this simplifies setting up the necessary tools to easily release new versions of every project using CD (instead of building locally on our laptops).

This project is the "source of truth" for the shared Makefile modules used in the cert-manager side-projects.

In this issue, we will track the progress of migrating all our side-projects to use "Makefile modules":

• approver-policy
  Migrate makefiles and CI/CD approver-policy#306
• istio-csr
  Migrate makefiles and CI/CD istio-csr#221
• csi-driver
  Migrate makefiles and CI/CD csi-driver#161
• csi-driver-spiffe
  Migrate makefiles and CI/CD csi-driver-spiffe#62
• google-cas-issuer
  Migrate to use Makefile modules google-cas-issuer#120
• cmctl
  https://github.com/cert-manager/cmctl
• issuer-lib
  Migrate makefiles and CI/CD issuer-lib#75
• cert-manager
  Move tools and generate/ verify to Makefile modules cert-manager#6749
• trust-manager
  Make Makefiles reusable and automate release process trust-manager#195
• openshift-routes
  Migrate the project to Makefile modules and release v0.6.0-alpha.0 openshift-routes#60
• csi-lib [not started yet]