manifest: introduce new `resolve` sub command

[Dentrax]

Description

It would be great to have a new resolve as a sub command of manifest. What I want to achieve is that ability to do kbld -f deployment.yml but in cosign itself:

# BEFORE
image: index.docker.io/*username*/foo:v0.1.0

# AFTER
image: index.docker.io/*username*/foo@SHA256-REPLACED

Support list:

KIND	IMAGE PATH
Deployment	spec.template.spec.containers[*].image
DaemonSet	spec.template.spec.containers[*].image
ReplicaSet	spec.template.spec.containers[*].image
StatefulSet	spec.template.spec.containers[*].image
CronJob	spec.spec.template.spec.containers[*].image

manifest verify command firstly introduced in issue https://github.com/sigstore/cosign/issues/437 by @developer-guy. This is something part 2 to extend abilities of manifest command.

UX:

Single file:

$ cosign manifest resolve -f deployment.yaml -o resolved.yaml

You can give folder directly and apply:

$ cosign manifest resolve -f ./manifests | k apply -f -

Implementation

There are possible two ways to handle this:

1. Use kbld resolve as a library.

2. Integrate custom resolver as we did for Dockerfile: https://github.com/sigstore/cosign/pull/1120

I think this idea have been discussed somewhere else but I couldn't find where so opening this.