Adds support for allowing a RestoreItemAction to skip item restore

[sseago]

Fixes #1335

Adds support for allowing a RestoreItemAction to skip item restore

This allows a RestoreItemAction plugin to signal to velero that
the returned item should be skipped rather than restored to the
cluster.

To support this, a boolean SkipRestore attribute is added to
RestoreItemActionExecuteOutput. If restore.restoreResource finds
this set to true, any remaining actions on this item are skipped,
and restore on this item is skipped. Execution continues with
the next item of this resource type.

To signal this for a particular item, the RestoreItemAction's
Execute method should call WithoutRestore() on the
RestoreItemActionExecuteOutput before returning it.

The autogenerated code may need to be redone. I don't know if I'm using the wrong protoc version or missing a flag of some sort, because it changed a lot more than just around the code changes for this PR.

[sseago]

Addresses #1335

[sseago]

In our velero fork repo, instead of the full "Autogenerated code to support SkipRestore" commit, I applied a much smaller commit, basically just taking the subset of protoc-generated output that was relevant to my code changes. Instead of a bunch of changes across several files, it only modifies one file, adding SkipRestore to type RestoreItemActionExecuteResponse, and adding func (m *RestoreItemActionExecuteResponse) GetSkipRestore() bool while discarding all the other changes from hack/generate-proto.sh. So far everything seems to work with this more limited commit, but I wasn't sure which approach was recommended

[skriss]

Thanks for the PR @sseago! Generally looks reasonable to me. I recall someone else having similar issues when updating proto - one note is that you need to use the protoc plugin protoc-gen-go v1.0.0 -- which is not the latest version. These instructions may help. Separately, we should probably both containerize and update the go plugin for proto updates.

@carlisia, please take a look as well.

[skriss]

Output of protoc --version for me:

libprotoc 3.6.1

[skriss]

I did a quick proto update with the field you added - you can grab skriss@2293e00 if that's easier

[sseago]

@skriss Looks like grabbing protoc-gen-go v1.0.0 was all I needed. My proto output now matches the one you linked above.

[sseago]

I've made the suggested changes and fixed the generated code output.

[carlisia]

This looks good, very useful 👍

[skriss]

LGTM. @carlisia, note we should do another update to the plugin-example repo to capture this.