Better middleware injection

[geospatial-jeff]

The current middleware injection makes it difficult for users to configure the middleware they are injecting, see https://github.com/stac-utils/stac-fastapi/pull/341 and https://github.com/stac-utils/stac-fastapi/pull/341#issuecomment-1201581834.

There is no real advantage to abstracting middleware here, should just let the user configure and attach their own while providing sensible defaults.