feat: add nextjs skeleton for the ui

[kayra1]

Description

Main UI Code

This is a nextjs UI skeleton which is served by the gocert application located in the UI folder. Simply do:
bun i / npm i
and
bun run build / npm run build

to produce an out/ folder that contains the static assets for the frontend. This directory is then served up.

CI for the frontend

On top of the usual CI, there is now a step to build the website to make sure that the rock will build without issue, and there is another step to run the component tests for the nextjs application.

Build

Building uses the mechanism nextjs provides. There is first class IDE support for this option.

Testing

The nextjs app is tested using vitest, which does component level tests. Each test output reports directly to github actions, giving embedded test response messages:

The ROCK

The ROCK now has an extra step to build the UI from within gocert in the build step, and go's installer will copy over the necessary assets.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that validate the behaviour of the software
• I validated that new and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules