Optional ability to check if client has permissions to perform CRUD actions before trying them

[ncdc]

Describe the problem/challenge you have
When reconciling an App and making changes to a cluster, kapp immediately tries to perform all the CRUD changes. If/when it encounters an error, it stops immediately. This can leave the content on the cluster in some intermediate or unknown state.

Describe the solution you'd like
Add an optional field to the App spec to allow the user to indicate they'd like kapp to check if the client (service account or cluster credentials) has permissions to perform every operation needed before executing any of them. If any of the checks fails, kapp makes no modifications to the cluster and returns an error.

Anything else you would like to add:
The SubjectAccessReview API can be used for these checks.

The related kapp issue is carvel-dev/kapp#855.

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[100mik]

We do have access to al the GVKs we need CRUD on before we actually deploy. In theory, we could do SubjectAccessReviews on these in the diffing phase if a certain flag is provided 🤔

[praveenrewar]

(Related slack thread)

[everettraven]

@100mik @praveenrewar Now that there is a preflight check for this in kapp as of carvel-dev/kapp#887 is there anything left to do for this functionality besides waiting for a new release of kapp?

It looks like the App resource already has an option to pass in a set of raw options via the App.spec.deploy.kapp.rawOptions field that can be used to enable/disable preflight checks

[praveenrewar]

@everettraven We have a list of kapp flags that are allowed in kapp-controller. We need to add the preflight flag in there while bumping the kapp version in kapp-controller.