Implements a DELETE API endpoint for stopping a graph monitoring process and refactors the graph API tests

Adds API endpoint to continuously execute the graph workflow - implements error handling functionality only

Moves SDN controller and SFEMC port numbers out of implementation - passed to CLMC as environment variables, default 8080 port used if not passed

Modified the build_network_graph API endpoint to read the sr-cluster mappings from a file - temporary solution

Updates CLMC to always set the HTTP Accept header to application/json - otherwise, error messages might be sent as HTML

Separated configuration API calls from starter API calls - /aggregator/config and /aggregator/status

POST request to /aggregator now configures all the settings including database name and url, report period and running status (on/off)