Convert engine constants to configuration

Is your feature request related to a problem? Please describe. The current SMARTS engine does not allow for configuration of important features. We would like to go through parts of the engine and convert settings to

Describe the solution you'd like Go through parts of the engine and replace areas where configuration is useful:

• Add an engine configuration document to readthedocs
  • List out what features have been made configurable
  • List out where configuration can be found
• Update configuration

Some examples of useful configuration are: SMARTS_SENSOR_WORKER_COUNT,

Additional context See the PR where the utility was added for additional context: #1828