Added metadata to dataelement

[walldenfilippa]

Description

Added metadata to the data element, along with functionality to store the metadata within it.
Additional functionality in app-lib (Altinn/app-lib-dotnet#1531) and frontend(Altinn/app-frontend-react#3797). Storage is in process.

Related Issue(s)

• #{issue number}

Verification

• Your code builds clean without any errors or warnings
• Manual testing done (required)
• Relevant automated test added (if you find this hard, leave it and we'll help out)
• All tests run green

Documentation

• User documentation is updated with a separate linked PR in altinn-studio-docs. (if applicable)
• I'll complete the documentation once the work is finished.