Customizations in custom-src are now npm packages

[richard-cox]

Stratos customizations were previously in ./custom-src and included in the build via symlinks. These customizations have now moved into local npm packages located in ./src/frontend/packages. For more details please see our customization documentation at ./website/docs/extensions/introduction.md or https://stratos.app/docs/extensions/introduction. There you will also find instructions on migrating to npm packages and a tool to help automate most of the process.