feat(app) RHIDP-1803 enable field extensions

[gashcrumb]

Description

This commit enables support for Scaffolder field extensions. A plugin
can export a field extension as documented and then configure it to be
included in the list of enabled scaffolder field extensions using the
following configuration:

dynamicPlugins:
  frontend:
    my-plugin:
      scaffolderFieldExtensions:
        - importName: SomeExportedFieldExtension

Which issue(s) does this PR fix

• Fixes RHIDP-1803
• Fixes Support to register scaffolderPlugin.provide(createScaffolderFieldExtension( for dynamic plugin #1146

PR acceptance criteria

Please make sure that the following steps are complete:

• GitHub Actions are completed and successful
• Unit Tests are updated and passing
• E2E Tests are updated and passing
• Documentation is updated if necessary (requirement for new features)
• Add a screenshot if the change is UX/UI related

How to test changes / Special notes to the reviewer

There's a really simple extension in this package that can be used for a quick test. You can import this template and then use this configuration:

dynamicPlugins:
  frontend:
    backstage-plugin-simple-test-components:
      scaffolderFieldExtensions:
        - importName: SimpleTestFieldExtension

[openshift-ci]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[github-actions]

The image is available at: quay.io/janus-idp/backstage-showcase:pr-1253!

[davidfestal]

/approve

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[davidfestal]

/lgtm

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: davidfestal

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[github-actions]

The image is available at: quay.io/janus-idp/backstage-showcase:pr-1253!

[cmoulliard]

We cannot retest the image published as we got such issues using guest auth provider. See screenshots hereafter

[cmoulliard]

I was able to launch janus-idp locally using as auth provider .... github

auth:
  environment: development
  providers:
    #  guest: {}
    github:
      development:
        clientId: fde4...080e
        clientSecret: 8ba...0f20

The fieldExtensions are working if we add as config

dynamicPlugins:
  rootDirectory: dynamic-plugins-root
  frontend:
    qshift.plugin-quarkus:
      scaffolderFieldExtensions:
      - importName: QuarkusExtensionListField
      - importName: QuarkusVersionListField
      - importName: QuarkusQuickstartPickerField

[gashcrumb]

That's great news @cmoulliard! This will need plenty of testing as I've only tried the most minimal use case, so raise issues if you run into anything. Thanks!