Check-in testdata such that test can be run in IDE/ using go without using Makefile

[inteon]

Alternative solution for cert-manager/makefile-modules#209.
Makes it possible to run Go tests without Makefile (eg. when running using IDE).

Checks-in the testdata instead of generating on demand as part of the Makefile target.

cc @erikgb

[cert-manager-prow]

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[erikgb]

The proposed changes will solve my immediate issues, but I am bit worried about the make target dependencies. If I modify the API in Go source code or modify the "testdata" CRD and then run make generate-crds, the "testdata" CRD is not updated. This could be not very clear for users. Do you see a way to fix this with your proposed solution?

We should at least ensure that the "testdata" CRD is up-to-date in CI, but that is maybe OK? Not sure how the verfy-generated mechanism actually works.

[inteon]

The proposed changes will solve my immediate issues, but I am bit worried about the make target dependencies. If I modify the API in Go source code or modify the "testdata" CRD and then run make generate-crds, the "testdata" CRD is not updated. This could be not very clear for users. Do you see a way to fix this with your proposed solution?

We should at least ensure that the "testdata" CRD is up-to-date in CI, but that is maybe OK? Not sure how the verfy-generated mechanism actually works.

When I update eg. types_bundle.go and run make generate, I get the following result:

$ git status
On branch simplify_go_test
Your branch is up to date with 'inteon/simplify_go_test'.

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
        modified:   deploy/charts/trust-manager/templates/crd-trust.cert-manager.io_bundles.yaml
        modified:   pkg/apis/trust/v1alpha1/types_bundle.go
        modified:   test/testdata/trust.cert-manager.io_bundles.yaml

no changes added to commit (use "git add" and/or "git commit -a")

Both the deploy/charts/trust-manager/templates/crd-trust.cert-manager.io_bundles.yaml and test/testdata/trust.cert-manager.io_bundles.yaml file got updated + CI should check that they are kept up-to-date.