[DwC export]: Add EML creation/import mechanism for Export Packages

[grantfitzsimmons]

Goal

Provide a straightforward way for users to create or import Ecological Metadata Language (EML) when setting up an Export Package, minimizing friction.

Background

Every valid DwCA must include an EML file. Users can create one via the GBIF EML generator and import it directly into the Export Package form.

Acceptance Criteria

• In the Export Package form, the Metadata field has an Import EML button.
• Clicking Import EML opens a file picker to upload a locally saved .xml EML file.
• On upload, the EML is saved as a new spappresource record and linked to the Export Package.
• A Generate EML button/link opens the GBIF EML generator (https://gbif-norway.github.io/eml-generator-js) in a new browser tab.
• The imported EML is validated; if it fails basic format checks, an error is shown.
• The EML produces output that passes the GBIF data validator when included in the DwCA.