Enable sort_key for sorting results

[abarciauskas-bgse]

👋🏽 both collections and granules allow for sorting results by a sort key (see https://cmr.earthdata.nasa.gov/search/site/docs/search/api.html#sorting-collection-results). It would be great to add this parameter to search_data for sorting granule results by something like start_date or end_date.

Example:

first_result = earthaccess.search_data(
    short_name=short_name,
    cloud_hosted=True,
    count=1,
    sort_key='+end_date'
)

last_result = earthaccess.search_data(
    short_name=short_name,
    cloud_hosted=True,
    count=1,
    sort_key='-end_date'
)