Update pystac migrate for STAC spec 1.1.0

[jsignell]

pystac provides tools for migrating that walk the cataolog and migrate the STAC version and the extension versions. So those functions will need to be updated for this new version of STAC.

[jsignell]

It was mentioned in the STAC call today that stac-migrate and stac-rs both have versions of the migration code at this point. So that can be used as a jumping off point.

[jsignell]

Reading through https://github.com/stac-utils/stac-rs/blob/main/crates/core/src/migrate.rs it looks like the main changes are:

• bands (this will wait until Add bands #1238 - so pystac v2)
• license
• file:/// (this will wait until Add file:// to self links that don't have a protocol #1472 - so pystac v2)
• something to do with properties that I can't quite figure out

[gadomski]

something to do with properties that I can't quite figure out

That's just to make the license migration generic for all STAC things (we have to work on the properties dict for Items instead of the item itself).