add generic Dataset easyblock

[smoors]

(created using eb --new-pr)

depends on framework PR:

• add support for data installations easybuild-framework#4474

now also implements an "object storage" as suggested by @boegel . things i’m not sure about:

• currently uses symlinks to files in the object storage. should i use hardlinks instead, or add an option for it?
• the object storage is not required to get a working installation. should i add an option for it?

[jfgrimm]

reminder for myself to revisit RELION once this is merged: easybuilders/easybuild-easyconfigs#19678