chore(docs): start dynamic plugins FAQ

docs/dynamic-plugins/faq.md

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+# Frequently Asked Questions
+
+## What is Dynamic plugin derived package?
+
+This is a special JavaScript package that is derived from an original plugin package source code.
+It has `-dynamic` suffix in its name. Its purpose is to be dynamically loaded by the RHDH.
+This plugin shouldn't be pushed into the [public npm registry](https://www.npmjs.com), but it can be published to a private or internal npm registry.
+
+## How to configure up a dynamic plugin project to publish to an npm registry?
+
+**WARNING:** Do not push derivated dynamic plugin packages to the public npm registry. Push it to a private or internal npm registry only. If possible use OCI images or tgz files to distribute the derived packages instead of npm registry. <!-- TODO: link to documentation about packaging plugins as OCI images or tgzs  -->
+
+1. Generate plugin derived package by running the following command:
+
+  **NOTE:** If you are not using the latest RHDH version, see [versions](../versions) document to see which version of the `@janus-idp/cli` you should use.
+
+  ```sh
+  npx @janus-idp/cli@latest package export-dynamic-plugin
+  ```
+
+1. Publish the generated package to an npm registry:
+
+  ```sh
+  cd dist-dynamic
+  npm publish --registry <npm_registry_url>
+  ```
+
+Alernatively, you can add the following to your `package.json` before running `npx @janus-idp/cli@latest package export-dynamic-plugin`:
+
+```json
+{
+  "publishConfig": {
+    "registry": "<npm_registry_url>"
+  }
+}
+```
+
+and than just run `npm publish` inside the `dist-dynamic` directory.
+
+```sh
+cd dist-dynamic
+npm publish
+```
+
+## How to configure RHDH to use private or internal npm registry?
+
+See [Using a custom NPM registry](../dynamic-plugins#using-a-custom-npm-registry)
+
+## How to install community Backstage plugin to the RHDH?
+
+TODO
+
+## How make a scaffolder field extension?
+
+<!-- TODO: fix link once https://github.com/janus-idp/backstage-showcase/pull/1789 is merged -->
+
+This is documented at [Provide custom Scaffolder field extensions](../dynamic-plugins#provide-custom-scaffolder-field-extensions)
+
+## How to make a custom action?
+
+TODO
+
+## How to load a username transformer when ingesting catalog entities?
+
+TODO
+
+## How to properly migrate a plugin project and your local environment to Yarn 3.x?
+
+TODO