v2: bump chart to v5.9.15 to support full podtemplate overrides

[chrisseto]

Prior to this commit the podTemplate field of the redpanda operator had drifted out of sync with that of the helm chart. This prevented users from leveraging the new pod template overrides recently added.

This commit bumps the internal chart version to v5.9.15 updates the PodTemplate type to be a PodSpecApplyConfiguration.

[RafalKorepta]

=== RUN   TestDefluxedMinimumVersion
--
  | redpanda_types_test.go:82:
  | Error Trace:	/work/operator/api/redpanda/v1alpha2/redpanda_types_test.go:82
  | Error:      	"NOTE! Alpha feature\nUseFlux flag set to `false` will prevent helm controller from reconciling helm chart. The operator would be\ntight with `go` based Redpanda helm chart version. The rest of the ChartRef fields would be ignored.\n\nBefore setting UseFlux flag to `false` please alight your ChartVersion to at least `5.9.11`\nversion of the Redpanda chart.\n\nRedpandaStatus might not be accurate if flag is set to `false` and HelmRelease is manually deleted.\n\nTo achieve dynamic switch for Flux controllers (HelmRelease and HelmRepository) the resources\nwould not be removed, but they will be put in suspended mode (if flag is provided and set to `false`).\n\nhttps://fluxcd.io/flux/components/helm/helmreleases/#suspend\nhttps://fluxcd.io/flux/components/source/helmrepositories/#suspend" does not contain "5.9.15"
  | Test:       	TestDefluxedMinimumVersion
  | Messages:   	'useFlux' should reference the version "5.9.15" of the go.mod installed redpanda chart. Do you need to run 'task generate' or update the comment?
  | --- FAIL: TestDefluxedMinimumVersion (0.00s)

[andrewstucki]

The applyconfiguration embedding does blow up the CRD definition fairly massively, but 🤷 -- at this point we need the SSA anyway since the CRD is already quite large.

[chrisseto]

Yeah, I'm not sure what to do about that one :/ I was expecting the CRD to shrink a touch because apply configs don't include comments. Didn't realize it was such a big increase...