Create API service

[uniqueg]

Is your feature request related to a problem? Please describe.
In the spirit of the microservice architecture pattern, it would be beneficial to distribute TEStribute also as a deployable service that can be hosted independently of a workflow engine or workflow execution service.

Describe the solution you'd like
OpenAPI specifications should be devised that describe an endpoint that executes the rank_services() function. The input parameters and response should be defined as models (these could then also be reused in the TEStribute code for type checks etc). A very basic Connexion-based microservice could then be written to consume those specs. The service should be dockerized and the deployment/installation instructions added to the README.md.

Describe alternatives you've considered
N/A

Additional context
To operationalize this use case, a corresponding client (#26) would need to be implemented as well.