SE-2277 Adds infrastructure overview and diagram

Provides an overview of the various services OpenCraft maintains to support Ocim instances.

Testing instructions:

1. Read through added documentation for correctness and completeness.
2. Check links and diagram are correct.

Author notes and concerns:

1. This audience for this infrastructure documentation is potential Ocim clients and users of the system. It is not intended to replace OpenCraft's own internal documentation for using or maintaining these services.

Reviewers

• @itsjeyd