build: Download CRD deps only when necessary

[darkowlzz]

Create individual make targets for the CRD dependencies so that make can identify that the CRD dependencies have already been downloaded and skip. When the SOURCE_VER changes, old CRDs are deleted and new ones are
downloaded, keeping a record of the source CRD versions in build/.src-crd-<version> by file name.
Also, introduce cleanup-crd-deps make target to delete the previously downloaded CRDs.

Without this, the CRDs were downloaded every single time when running tests:

$ ls config/crd/bases/
buckets.yaml  gitrepositories.yaml  kustomize.toolkit.fluxcd.io_kustomizations.yaml  ocirepositories.yaml

# After removing the curl silence option from Makefile. 
$ make test
...
curl https://raw.githubusercontent.com/fluxcd/source-controller/v0.33.0/config/crd/bases/source.toolkit.fluxcd.io_gitrepositories.yaml > config/crd/bases/gitrepositories.yaml
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 38070  100 38070    0     0  31504      0  0:00:01  0:00:01 --:--:-- 31488
curl https://raw.githubusercontent.com/fluxcd/source-controller/v0.33.0/config/crd/bases/source.toolkit.fluxcd.io_buckets.yaml > config/crd/bases/buckets.yaml
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 24578  100 24578    0     0  66385      0 --:--:-- --:--:-- --:--:-- 66427
curl https://raw.githubusercontent.com/fluxcd/source-controller/v0.33.0/config/crd/bases/source.toolkit.fluxcd.io_ocirepositories.yaml > config/crd/bases/ocirepositories.yaml
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 17450  100 17450    0     0  16903      0  0:00:01  0:00:01 --:--:-- 16908
...

An alternative is to pass the curl continue-at option -C - which checks with remote and doesn't downloads the same file if it has been downloaded already:

curl -C - https://raw.githubusercontent.com/fluxcd/source-controller/v0.33.0/config/crd/bases/source.toolkit.fluxcd.io_gitrepositories.yaml -o config/crd/bases/gitrepositories.yaml
** Resuming transfer from byte position 38070
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
curl -C - https://raw.githubusercontent.com/fluxcd/source-controller/v0.33.0/config/crd/bases/source.toolkit.fluxcd.io_buckets.yaml -o config/crd/bases/buckets.yaml
** Resuming transfer from byte position 24578
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
curl -C - https://raw.githubusercontent.com/fluxcd/source-controller/v0.33.0/config/crd/bases/source.toolkit.fluxcd.io_ocirepositories.yaml -o config/crd/bases/ocirepositories.yaml
** Resuming transfer from byte position 17450
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0

But with individual make targets for the CRDs, there's no need to check if the downloaded files match with the remote. It's better to just skip downloading entirely if the file exists using make's native style.

For handling overall updates to such dependencies, it may be better to introduce a distclean make target that resets the repository, deleting any old files that need to be updated. Maybe later as a separate PR.

[darkowlzz]

I've pinned envtest kubernetes version to 1.25 in #784, which fixes the controller test failure due to the new HorizontalPodAutoscaler API.

[stefanprodan]

LGTM

Thanks @darkowlzz