Split _load_collection depending on FetchType

[GriffinBabe]

As this function is getting longer (which is why I get the creation of _load_collection_hybrid) we might consider splitting of the pre and post processing of the different fetchtypes. That way it might be easier to find the differences both as a user and future developer.
Not sure if this is in the scope of this PR however, we could create an issue for this.

Originally posted by @VictorVerhaert in #130 (comment)

[GriffinBabe]

https://github.com/Open-EO/openeo-gfmap/pulls#discussion_r1645666509