Live import preview should show all metadata values, not only the first one

[jensvannerum]

Description

This change makes is to the live import preview shows all metadata values present, not only the first one. This gives user a better idea of the item they are actually importing.

Instructions for Reviewers

This simply changes the single metadataValue object to a list of them and displays them with an ngFor

You can test this by:

• going to /mydspace
• selecting an external item for import
• open up the preview, verify you can see multiple values for the metadata fields (if present)

Checklist

• [x] My PR is small in size (e.g. less than 1,000 lines of code, not including comments & specs/tests), or I have provided reasons as to why that's not possible.
• [x] My PR passes ESLint validation using yarn lint
• [x] My PR doesn't introduce circular dependencies (verified via yarn check-circ-deps)
• [x] My PR includes TypeDoc comments for all new (or modified) public methods and classes. It also includes TypeDoc for large or complex private methods.
• [x] My PR passes all specs/tests and includes new/updated specs or tests based on the Code Testing Guide.
• [x] If my PR includes new libraries/dependencies (in package.json), I've made sure their licenses align with the DSpace BSD License based on the Licensing of Contributions documentation.
• [x] If my PR includes new features or configurations, I've provided basic technical documentation in the PR itself.
• [x] If my PR fixes an issue ticket, I've linked them together.