Update EGA manifest file to use new EGA download client (v3.1)

[hknahal]

Message on EGA's website (https://ega-archive.org/):

Dear Users, please be aware that the Java Client (API V2) will shortly be deprecated and replaced with a new API (V3.1) which is python based. This new version will be more robust and provide better functionality. Please monitor this banner and our twitter feed (@EGAarchive) for further updates and useful information - EGA team

The current downloadable manifest file (when searching in EGA-Hinxton repository) is a bash script that runs the Java EGA download client tool to download files. We'll need to update this script to use the new python EGA download client. There's no documentation released yet for v3.1, but I'll update this ticket when it becomes available.