Remove TODOs from comments

As discussed in #446, some kapp-controller structs have TODO comments that are then used as descriptions in schemas:
* https://github.com/vmware-tanzu/carvel-kapp-controller/blob/babe7624f2c72c54e5f83860df410470f2b1bd71/config/crds.yml#L227
* https://github.com/vmware-tanzu/carvel-kapp-controller/blob/babe7624f2c72c54e5f83860df410470f2b1bd71/config/crds.yml#L350
* https://github.com/vmware-tanzu/carvel-kapp-controller/blob/babe7624f2c72c54e5f83860df410470f2b1bd71/config/crds.yml#L360

The comment about supporting Docker config format was implemented in v0.19.0 of kapp-controller: https://carvel.dev/kapp-controller/docs/latest/app-overview/#image-and-imgpkgbundle-authentication. So this comment can be removed.

There is another question about removed the jsonnet/kustomize properties since they are not implemented. It may be confusing for users to see this information in the schema. We have not even decided if we will support these options yet, so we should consider removing them until they are implemented.

To update the schema descriptions above, the comments above the properties in the go structs need to be changed and then the build/generator scripts need to be run. An example of doing this would be as follows:

1. Update the comments:

https://github.com/vmware-tanzu/carvel-kapp-controller/blob/babe7624f2c72c54e5f83860df410470f2b1bd71/pkg/apis/kappctrl/v1alpha1/types_fetch.go#L46

2. Run `./hack/build.sh` to regenerate the crds.yml file

3. Run the generator scripts: `./hack/gen.sh` and `./hack/gen-apiserver.sh`. **NOTE:** protobuf must be installed to successfully run these scripts. See install directions for more information: https://grpc.io/docs/protoc-installation/.