Create [REST or RPC] API for Tern to run as a service on Kubernetes

[rnjudge]

Description
We would like to run Tern in some number of persistent containers as a service in a K8s cluster, scaled to the resource environment. Ideally, something calls out to the “Tern cluster” via its APIs and asks for work (i.e. the 100 containers names for scanning). Tern figures out how to load balance those across its available instances, perhaps with Kubernetes spinning up more worker instances of Tern container if resources are available or the quality of the Tern service gets to low.

To start, a GET call that could return Tern's JSON and SPDX JSON report would probably be a good place to start.

To Do
https://github.com/tern-tools/tern-api/issues/5

Background
Tern already has a web API repository. At this time, we're not sure how much of it could be re-used.
See also: #65, #1096

Super Issues
#1110