Support repository charts with unconventional .tgz filename

[jonasz-lasut]

Description of your changes

Fixes #336

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable to ensure this PR is ready for review.

How has this code been tested

Added new E2E test target and tested E2E "classic release" and the new release with unconventional tgz path
UPTEST_EXAMPLE_LIST="examples/namespaced/sample/release-nonconventional-tgz.yaml" make e2e
(/test-examples="examples/namespaced/sample/release-nonconventional-tgz.yaml" for the pipeline :))

Before (running provider-helm from main):

apiVersion: helm.m.crossplane.io/v1beta1
kind: Release
metadata:
  annotations:
    crossplane.io/external-create-failed: "2026-06-13T14:23:04Z"
    crossplane.io/external-create-pending: "2026-06-13T14:23:04Z"
    crossplane.io/external-name: node-feature-discovery
    upjet.upbound.io/test: "true"
  creationTimestamp: "2026-06-13T14:22:58Z"
  finalizers:
  - finalizer.managedresource.crossplane.io
  generation: 2
  name: node-feature-discovery
  namespace: crossplane-system
  resourceVersion: "1049"
  uid: 5aa194de-33ad-4a12-b74c-59d04c3e8fae
spec:
  forProvider:
    chart:
      name: node-feature-discovery
      pullSecretRef:
        name: ""
      repository: https://kubernetes-sigs.github.io/node-feature-discovery/charts
      version: 0.18.3
    namespace: nfd
  managementPolicies:
  - '*'
  providerConfigRef:
    kind: ClusterProviderConfig
    name: helm-provider-cluster
status:
  atProvider: {}
  conditions:
  - lastTransitionTime: "2026-06-13T14:22:58Z"
    observedGeneration: 2
    reason: Creating
    status: "False"
    type: Ready
  - lastTransitionTime: "2026-06-13T14:22:58Z"
    message: 'create failed: failed to install release: failed to load chart: stat
      /tmp/charts/node-feature-discovery-0.18.3.tgz: no such file or directory'
    observedGeneration: 2
    reason: ReconcileError
    status: "False"
    type: Synced

After changes:

apiVersion: helm.m.crossplane.io/v1beta1
kind: Release
metadata:
  annotations:
    crossplane.io/external-create-pending: "2026-06-13T14:27:57Z"
    crossplane.io/external-create-succeeded: "2026-06-13T14:27:59Z"
    crossplane.io/external-name: node-feature-discovery
  creationTimestamp: "2026-06-13T14:27:57Z"
  finalizers:
  - finalizer.managedresource.crossplane.io
  generation: 2
  name: node-feature-discovery
  namespace: crossplane-system
  resourceVersion: "962"
  uid: f5e68e30-cf23-4a57-b51b-a9a2461800ec
spec:
  forProvider:
    chart:
      name: node-feature-discovery
      pullSecretRef:
        name: ""
      repository: https://kubernetes-sigs.github.io/node-feature-discovery/charts
      version: 0.18.3
    namespace: nfd
  managementPolicies:
  - '*'
  providerConfigRef:
    kind: ClusterProviderConfig
    name: helm-provider-cluster
status:
  atProvider:
    releaseDescription: Install complete
    revision: 1
    state: deployed
  conditions:
  - lastTransitionTime: "2026-06-13T14:27:59Z"
    reason: Available
    status: "True"
    type: Ready
  - lastTransitionTime: "2026-06-13T14:27:59Z"
    observedGeneration: 2
    reason: ReconcileSuccess
    status: "True"
    type: Synced
  synced: true