2.0.0 clean-up

[m-mohr]

We (may have) introduced a number of changes that we made only for backward-compability and they should be removed in 2.0.0. A list of potential things to do:

• Remove language that requires all assets to be available in Collection Assets, see Job Results: STAC Collections instead of (or in addition to) Items #343 and Support STAC Collections as Job Results #359
• Remove /process_graphs/... endpoints, see Unification of /processes and /process_graphs #310 and Process unification #310 #348
• Remove support for STAC 0.9.0 and 1.0.0-beta/rc and update to STAC API 1.0 - remove all STAC version conditionals (e.g. type field, conformsTo, ...).
• Require type field in Collections (Collections and Batch Job Results as Collections) and Catalogs (GET /)
• Remove default billing plan from capabilities Clarify (default) billing plans #428, potentially move the whole billing part to the /me endpoint
• openeo:status in batch job results should be required Support partial/incomplete batch job results #430 #433 (comment)