fix: revert internal api to v2beta1

[raffis]

Current situation

flux-build v3 uses only the v2 api version of Helmreleases just as the helm-controller from flux v2.
However this was a poor design choice since this basically drops support for some features used in the beta apis such as postrender patches in the deprecated format.
While for a controller it makes sense to only work with a certain version (withouth conversion) for flux-build there is no reason to drop support as different apiVersions might be used at the same time and a controller only works with one.

Proposal

Partially revert the api changes and go back to the beta one. The advantage of the beta one is it supports both the deprecated and the new fields.
This change is fully backwards compatible, it only changes flux-build internals.

[coveralls]

Pull Request Test Coverage Report for Build 10938745220

Details

• 46 of 131 (35.11%) changed or added relevant lines in 5 files are covered.
• 5 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.08%) to 50.351%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
internal/helm/postrenderer/post_renderer_namespace.go	0	1	0.0%
internal/helm/postrenderer/post_renderer_origin_labels.go	5	9	55.56%
internal/helm/postrenderer/post_renderer.go	0	11	0.0%
internal/helm/postrenderer/post_renderer_kustomize.go	41	56	73.21%
internal/build/helm.go	0	54	0.0%

Files with Coverage Reduction	New Missed Lines	%
internal/build/helm.go	1	0.0%
internal/helm/postrenderer/post_renderer_origin_labels.go	2	64.71%
internal/helm/postrenderer/post_renderer_kustomize.go	2	74.56%

Totals
Change from base Build 10937017279:	-0.08%
Covered Lines:	1649
Relevant Lines:	3275

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💛 - Coveralls