Collection PATCH operation

[emmanuelmathot]

In a typical STAC API implementation, collections are "generated" from the items they contains.
extent and summaries fields should be therefore consistent with the items set and generated automatically.
However other fields:

• title
• description
• assets
• license
• links
• keywords
• providers

should be manageable from the API.
The PATCH operation is the best option to allow the update of those fields for a collection.