Tärpistö 3.0 -update

[FinThunderstorm]

As express-react-views is not maintained anymore (last updated from 4 years ago) and therefore blocks updating React to newer versions like to 18 from 16, is migration needed. This PR researches way to implement migration using Next.js's new app-folder structure with React Server Components.

Evolved into Tärpistö 3.0 -update.

[cxcorp]

Should we go for a merge?

[FinThunderstorm]

Not yet, there are currently coming more on my local repo that I have been lately working on.

"Quote of the day: https://github.com/vercel/next.js/issues/52837" - faced this bug while implementing modals.

[FinThunderstorm]

Status update:

• All main functionalities are transferred to Next.

Current blockers:

• https://github.com/vercel/next.js/issues/52837
• ~https://github.com/vercel/next.js/issues/52681~

Still needs some working:

• [ ] Add click modal outside to dismiss functionality
• [X] ~Check Docker build works and creates usable image~
• [X] ~Check Next related files for styling like errors etc~ ~-> Currently not-found elements is not even rendering itself even if it is defined right. Waits for checking if there is already bug report done. Also there is problems with notFound() in layout files, Next docs says it is fine to use it in generateMetadata, but it throws errors.~ Fixed. Looks likenotFound() problem was related to canary version.
• [X] ~Fix security check is not working and telling everything is pass even there are failures while running scan.~ -> Looks like it should be working. Results needs some looking for actions.
• [X] ~Handle flash messages.~ -> There is currently no possibility to return errors in server-component only manner. redirect() does not take any headers as parameters and returning new NextResponse.redirect() etc is not allowed in Server Actions.
• [X] ~Fix modal close button after blocker bugs are fixed~
• [X] ~Check tests are working after latest updates~ -> Last errors are waiting for intercepting routes modal bug to be fixed.
• [X] ~Use Next's possibility to move files into src folder~
• [X] ~Investigate self-hosted Renovate in GHA to be runned against master branch~ -> In scope of own PR.

[FinThunderstorm]

Current status

Features missing

• Flash messages. Currently not possible to implement with server actions used in server components.

[FinThunderstorm]

Ready for production after testing in staging with production-like environment.

All conflicting files (package.json, package-lock.json, src/common.ts, src/config/index.ts and src/download.ts) are overwritten by this update.

[FinThunderstorm]

Went through the comments and made some changes. All comments have mentions if evolved into changes.