[Feature] standardise pooch registries for atlases generated from many files

[alessandrofelder]

Is your feature request related to a problem? Please describe.
When generating atlases, there is no standard, good way to check the has

We've encountered this problem several times

• axolotl atlas (we hard-coded the expected hashes into the source code, but this scales badly) Add Axolotl Pooch hash  #347
• catlas (no solution yet) new atlas file added - for cat #403
• kim dev ccf atlas (currently ignores hashes) Add all Kim's DevCCFv1 atlases #441

Describe the solution you'd like
I'd suggest

• calculating the hashes once (when we first package the atlas) and saving them into a file, using pooch.make_registry
• committing said file in a subfolder of /atlasgeneration
• the atlas generation script should then check hashes against the hashes in the file