Transaction Extension: purpose of the collection_id path parameter

[drnextgis]

What is the purpose of {collection_id} path parameter? It seems we can put an arbitrary value there and stac-fastapi will take collection name from the body.

Since there is no way to specify collection_id via UI it uses {collection_id} as it is 🤷‍♂️

[duckontheweb]

The STAC Spec also requires that a link with a rel type of collection be present if the collection property is present. This means that if you are using something like pystac.Item.validate to validate Items prior to insertion you have to add that link, even though it is going to be replaced by the backend anyway.

It seems like the desired behavior here would be:

1. Use the collection_id path parameter from the request if there is no collection property in the body or if that property is present and matches the path parameter
2. Raise an exception if the collection property is present and does not match the path parameter.