Introduce artifact max size limit of 50MiB

[stefanprodan]

Add a controller flag named --artifact-max-size=<bytes> with the default value of 50MiB. To disable the limit, the value can be set to --artifact-max-size=-1.

⚠️ Breaking change

The flag enforces a max size limit for the artifact contents produced by source-controller, to avoid out-of-memory crashes of consumers such as kustomize-controller.

Closes: #901