Consider upgrading CRDs by default in HelmReleases

Summary

While working on !3238 (merged), we realized that CRDs are not installed/upgraded by HelmReleases by default. We should consider enabling that feature by default in next release:

$ k explain helmrelease.spec.upgrade.crds
GROUP:      helm.toolkit.fluxcd.io
KIND:       HelmRelease
VERSION:    v2

FIELD: crds <string>
ENUM:
    Skip
    Create
    CreateReplace

DESCRIPTION:
    CRDs upgrade CRDs from the Helm Chart's crds directory according
    to the CRD upgrade policy provided here. Valid values are `Skip`,
    `Create` or `CreateReplace`. Default is `Skip` and if omitted
    CRDs are neither installed nor upgraded.
    
    
    Skip: do neither install nor replace (update) any CRDs.
    
    
    Create: new CRDs are created, existing CRDs are neither updated nor deleted.
    
    
    CreateReplace: new CRDs are created, existing CRDs are updated (replaced)
    but not deleted.
    
    
    By default, CRDs are not applied during Helm upgrade action. With this
    option users can opt-in to CRD upgrade, which is not (yet) natively
    supported by Helm.
    https://helm.sh/docs/chart_best_practices/custom_resource_definitions.