Simplify openeo.udf.feature_collection.FeatureCollection

[soxofaan]

FeatureCollection in the openeo.udf.feature_collection package was a direct copy of https://github.com/Open-EO/openeo-udf/blob/master/src/openeo_udf/api/feature_collection.py, including some things that look over-engineered or are unused as far as I know:

• constructor requires a id as (first) argument, but I have no idea where this is used, or at least which important aspect makes it a required first argument
• it also takes start_times and end_times, but I have never seen this being used, and I guess this kind of data can easily (and more flexibly) be included in the geopandas dataframe directly