fix: duplicate helm extensions in clusterconfig

[emosbaugh]

What this PR does / why we need it:

Vendor provided helm extensions may be duplicated in the cluster config in some scenarios. For example in the bundle from this run.

https://github.com/replicatedhq/embedded-cluster/actions/runs/11076879363/job/30781413202?pr=1241

        - chartname: /var/lib/embedded-cluster/charts/ingress-nginx-4.8.3.tgz
          name: ingress-nginx
          namespace: ingress-nginx
          order: 110
          timeout: 0
          values: |
            controller:
              service:
                type: NodePort
                nodePorts:
                  http: "80"
                  https: "443"
              image:
                digest: ""
                digestChroot: ""
              admissionWebhooks:
                patch:
                  image:
                    digest: ""
          version: 4.8.3
        - chartname: /var/lib/embedded-cluster/charts/goldpinger-6.1.2.tgz
          name: goldpinger
          namespace: goldpinger
          order: 111
          timeout: 0
          values: ""
          version: 6.1.2
        - chartname: /var/lib/embedded-cluster/charts/ingress-nginx-4.8.3.tgz
          name: ingress-nginx
          namespace: ingress-nginx
          order: 110
          timeout: 0
          values: |
            controller:
              service:
                type: NodePort
                nodePorts:
                  http: "80"
                  https: "443"
              image:
                digest: ""
                digestChroot: ""
              admissionWebhooks:
                patch:
                  image:
                    digest: ""
          version: 4.8.3
        - chartname: /var/lib/embedded-cluster/charts/goldpinger-6.1.2.tgz
          name: goldpinger
          namespace: goldpinger
          order: 111
          timeout: 0
          values: ""
          version: 6.1.2

Which issue(s) this PR fixes:

Does this PR require a test?

Does this PR require a release note?

Does this PR require documentation?

[github-actions]

This PR has been released (on staging) and is available for download with a embedded-cluster-smoke-test-staging-app license ID.

Online Installer:

curl "https://staging.replicated.app/embedded/embedded-cluster-smoke-test-staging-app/ci/appver-dev-e31e86f" -H "Authorization: $EC_SMOKE_TEST_LICENSE_ID" -o embedded-cluster-smoke-test-staging-app-ci.tgz

Airgap Installer (may take a few minutes before the airgap bundle is built):

curl "https://staging.replicated.app/embedded/embedded-cluster-smoke-test-staging-app/ci-airgap/appver-dev-e31e86f?airgap=true" -H "Authorization: $EC_SMOKE_TEST_LICENSE_ID" -o embedded-cluster-smoke-test-staging-app-ci.tgz

Happy debugging!