Make the general and dataset-details Export panes consistent

[mbaumann-broad]

Discussed in Slack here.

Currently, File Manifest export is on the dataset-details Metadata pane.
Moving that to the Export pane is more consistent with the general export page.

(With ff=verabim enabled) the dataset-details Export pane would then look like the general export page:

[MillenniumFalconMechanic]

See mocks (and UI background).

[NoopDog]

Hi @frano-m, this is approved to develop!

[frano-m]

To consider:

• Handling of user log in and log out.
• Loading states.