fix(backend-dynamic-feature-service): improve package resolution for bundled dynamic plugins

Updated `resolvePackagePath` to correctly resolve `package.json` for dynamic plugins that bundle their own copy of `@backstage/backend-plugin-api`. This change ensures that the resolution works for both the host application and bundled dependencies, enhancing compatibility with plugins created using the `backstage-cli package bundle` command.

Signed-off-by: David Festal <dfestal@redhat.com>
Assisted-by: Cursor

docs/tooling/cli/03-commands.md

@@ -38,7 +38,6 @@ The `package` command category, `yarn backstage-cli package --help`:
 ```text
 start [options]                  Start a package for local development
 build [options]                  Build a package for production deployment or publishing
-bundle [options]                 Bundle a plugin for dynamic loading (backend or frontend)
 lint [options] [directories...]  Lint a package
 test                             Run tests, forwarding args to Jest, defaulting to watch mode
 clean                            Delete cache directories
@@ -207,6 +206,11 @@ Options:
 
 ## package bundle
 
+:::caution Experimental
+This command is experimental and may receive breaking changes in future releases
+without a deprecation period. It is hidden from the main `--help` output.
+:::
+
 Bundle a plugin for dynamic loading. This creates a self-contained plugin
 package that can be deployed independently and loaded dynamically by a Backstage
 application. Supports both backend and frontend plugins.