Migrate the Frontend Coder Plugin to NFS

[camilaibs]

Description

This pull request migrates the Coder frontend plugin to support the new Backstage frontend system.

• The migrated plugin is available at a new "alpha" subpath, to ensure the legacy plugin exports remain unchanged;
• The Backstage Yarn Plugin was used to help in managing dependencies versions and ensure compatibility with the new frontend system;
• Added documentation on how to install and configure the plugin for Backstage applications that support the new frontend system;
• The app for local testing was also updated to run the new alpha version of the plugin. No visual changes are expected, here's how the plugin looks in the dev app.

Entity Card

After merging this pull request it would be nice to:

• Monitor alpha usage and gather feedback
• Plan deprecation timeline for legacy exports
• Update documentation with migration guide
• Consider promoting alpha to stable in future release

[camilaibs]

This file is used by "msw" to intercept requests that should be mocked by the Backstage dev app, such as requests to Coder Proxy API. The mock service worker needs to be in this "public" folder so that the Backstage CLI can find it and serve it at localhost:3000/mockServiceWorker.js.

[camilaibs]

This filter specifies that the card should be displayed for all entities of the component kind. Is there any specific entity spec that must also be present in the entity data for the card to be displayed?