build: fix test-integration

[n-losse]

Summary

Fixes make test-integration which was broken for several reasons accumulated since the script was last tested against the current build system and Crossplane v2.

Fixes

Build system mismatches

• HELM3 is not exported by the build system (it exports HELM); renamed throughout the script and in the Makefile prerequisite — without this, the helm binary was never downloaded and the variable was always empty
• KIND_NODE_IMAGE_TAG ?= v1.29.0 added to the Makefile so the value is defined before being passed to the script via KIND_NODE_IMAGE_TAG=${KIND_NODE_IMAGE_TAG}; previously it would expand to empty, causing kind to use kindest/node: with no version
• CONTROLLER_IMAGE incorrectly included a -controller- infix that no image in this repo is built with; corrected to match the actual image name produced by make build
• PACKAGE_CONTROLLER_IMAGE used ${DOCKER_REGISTRY}/ unconditionally, producing an invalid leading-slash reference when DOCKER_REGISTRY is empty; replaced with ${DOCKER_REGISTRY:+${DOCKER_REGISTRY}/}. The variable is now unused — the controller image is loaded into kind directly under its build name — but kept for potential external use
• helm repo add now passes --force-update so repeated runs don't fail if the repo is already registered

Crossplane v2 package cache

• The old code used up xpkg xp-extract --from-daemon on the controller runtime image, which is not a crossplane package — this produced an empty (EOF) cache file. Changed to crossplane xpkg extract --from-xpkg against the .xpkg file produced by make build.
• Crossplane v2 added a CEL validation rule requiring spec.package to be a fully qualified OCI reference (registry.example.com/repo/name:tag or @digest). The previous value "provider-template" is rejected. The fix uses the non-routable hostname xpkg.crossplane.internal with a zeroed digest (sha256:0000...), which passes validation and causes Crossplane to skip the registry HEAD request and go straight to the local cache.
• The cache filename is now computed to match crossplane-runtime's FriendlyID(source, digest) formula — truncate(source, 50) + "-" + truncate(digest, 12), DNS-label sanitized — so Crossplane can locate the extracted package.

Controller image for the provider pod

• xpkg extract produces only the package metadata (CRDs, crossplane.yaml); it does not preserve the embedded runtime image. Crossplane therefore falls back to using the package OCI reference as the pod image, which does not exist in the kind cluster. A DeploymentRuntimeConfig is now created alongside the Provider to override the pod image to the locally loaded controller image, following the same pattern used by build/makelib/local.xpkg.mk.