Further align with STAC 1.1

[soxofaan]

The "license" field of collection metadata is currently:

Alternatively, use proprietary if the license is not on the SPDX license list or various if multiple licenses apply.

The spec of STAC collections currently has (since radiantearth/stac-spec@7c2fad3):

String with the value other if the license is not on the SPDX license list. The strings various and proprietary are deprecated.

probably needs some alignment

[m-mohr]

See also #593