fix: refactor catalog polling to use updateStrategy field

[exdx]

Description of the change:
Updates the catalog source spec to change the polling field. Continuation of #1161. Example of new spec:

spec:
  displayName: CatalogSource Test
  sourceType: grpc
  image: quay.io/olmtest/catsrc-update-test:test
  updateStrategy:
    registryPoll:
      interval: 2m

Motivation for the change:
updateStrategy is more generic and will be useful when adding additional update sources in the future. There was an attempt to look at union types and try to implement the update strategy as a union struct but we did not find that the latest controller-tools supported union types at this time.

Reviewer Checklist

• Implementation matches the proposed design, or proposal is updated to match implementation
• Sufficient unit test coverage
• Sufficient end-to-end test coverage
• Docs updated or added to /docs
• Commit messages sensible and descriptive

[exdx]

/test unit

[ecordell]

Shouldn't we update this doc too? https://github.com/operator-framework/operator-lifecycle-manager/blob/master/doc/design/catalog-polling.md

[exdx]

/retest

[ecordell]

/lgtm

[openshift-ci-robot]

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[ecordell]

/refresh

[exdx]

/retest

[exdx]

/test unit

[exdx]

/test unit

[exdx]

/retest

[exdx]

/test e2e-aws-olm