Additionnal import v1

This merge request add the additional import to an existing table feature.

The feature is available in the view menu:

This feature reuses the existing file import modal for table creation and adds a sidebar to allow to configure field mapping between the imported file and the existing table.

What is missing:

• There is no lock yet to prevent user action while an import is in progress so if a user quickly change the field type or permanently delete a field the import is going to fail. -> Waiting for the lock mechanism
• The file import preview is text only and doesn't reflect the mapping -> postponed to next iteration

Merge Request Checklist

• changelog.md has been updated if required
• New/updated Premium features are separated correctly in the premium folder
• The latest Chrome and Firefox have been used to test any new frontend features
• Documentation has been updated
• Quality Standards are met
• Performance: tables are still fast with 100k+ rows, 100+ field tables
• The redoc API pages have been updated for any REST API changes
• Our custom API docs are updated for changes to endpoints accessed via api tokens
• The UI/UX has been updated following UI Style Guide

Closes #342 (closed)