Update COP-30 Search to Pull DEM

[Jack-Hayes]

Update coincident.search.search(dataset='cop30') to return 2021 DEM of the bbox of an input geometry (GeoDataFrame or GeoSeries). Maybe returned clipped raster and print distribution statistics too?

Building off of code below:

catalog = pystac_client.Client.open(
    "https://planetarycomputer.microsoft.com/api/stac/v1",
    modifier=planetary_computer.sign_inplace,
)
search = catalog.search(collections=["cop-dem-glo-30"], 
                            bbox=bbox)
items = search.item_collection()

Related: #23