Add CQL2 filter parameter for Authorization

[philvarner]

Related Issue(s):

• Add support for "hidden" filter in search endpoints for authorization restrictions #863
• Add support for "hidden" filter in aggregation endpoints for authorization restrictions #864

Proposed Changes:

1. Add a "hidden" CQL filter parameter
2. Organize most of the api.js functions to have consistent argument order
3. Add support for a header STAC-collections-authx to work in concert with the existing _collections parameter
4. Deprecate existing X-STAC-Endpoint header in favor of STAC-Endpoint, which conforms to RFC recommendations.

PR Checklist:

• I have added my changes to the CHANGELOG or a CHANGELOG entry is not required.