"Add Dataset" is not used in dashboard_datasets

[A-Souhei]

Description

We use "Create new dataset" on the "My account" page but "Add Dataset" on the "Find Data" page, let's use "Add Dataset" for both.

Closes fjelltopp/zarr-ckan#171

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[ChasNelson1990]

Sorry, is this another one that maybe belongs in fjelltopp-theme?