Make ApiServerSource v1 the stored version and add a migration tool

[capri-xiyue]

Problem
In 0.19, we promoted ApiServerSource to v1.
This is to track that we should make v1 the storage version for 0.20, and we should add a migration tool for it.
Similar to: https://github.com/knative/eventing/blob/master/config/pre-install/v0.16.0/storage-version-migration.yaml.
(May need to avoid using pre-install and try to use post-install)

Persona:
Which persona is this feature for?

Exit Criteria
ApiServerSource in v1 and able to migrate

Time Estimate (optional):
How many developer-days do you think this may take to resolve?

Additional context (optional)
#4166

Time Estimate (optional):
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Additional context (optional)
Add any other context about the feature request here.

[lberk]

@capri-xiyue are you aware of anything that require the need for a pre-install job? We're trying to avoid those for upcoming releases, instead, focusing on only using post-installs. Thanks!

[capri-xiyue]

@capri-xiyue are you aware of anything that require the need for a pre-install job? We're trying to avoid those for upcoming releases, instead, focusing on only using post-installs. Thanks!

Based on my understanding, https://kubernetes.io/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definition-versioning/#upgrade-existing-objects-to-a-new-stored-version, it looks like the upgrade of storage version can be done as a post-installs.
I was just following the previous upgrade procedure when I created this issue.

[pierDipi]

/assign