Improve init-app goal/task to use compatible version of frontend dependencies with the Hilla version

[taefi]

Is your feature request related to a problem? Please describe.

Using hilla:init-app on a bare-bone hilla project e.g. coming from Spring Initializr, has the following set backs:

• The version of frontend dependencies in package.json and package-lock.json can be incompatible with the Hilla version coming from pom.xml. This might result in a long waiting time while installing node_modules.
• Since there is no theming in the application, the application does not look nice.

Describe the solution you'd like

The desired solution is to generate the package.json and package-lock.json with a compatible version of frontend dependencies with the version of Hilla in the pom.xml.

Also, it would be nice to initialize the theming by adding:

• needed assets in frontend/themes/demo-theme
• a class implementing the AppShellConfigurator and annotated with @Theme("demo-theme") ("demo-theme" can be any arbitrary names)

[cromoteca]

In general, the versions used in Spring Initializr and in our skeletons should be aligned, but generated PRs need to be merged manually, so it can happen that users get different versions. This is a UX issue and we should investigate how to keep them in sync as much as possible. Let's also add the proposed theme class.