Align/map templates to HTAN

[anngvu]

Issue after seeing #168.

Basically, NF doesn't have templates at different data levels like HTAN, e.g. ScRNA-seqLevel1. Instead we default to just the lowest (rawest) level (because that is what's usually asked for).

This is fine for now, but later if we have more templates and want to make them more understandable in terms of HTAN, we should have better mappings and alignment.

Also, we don't have to call templates Level1, Level2, etc. like HTAN, but just have documentation/clear relationships for which template is for what type of raw/processed (which can be more understandable than something abstract like "Level 1").