Multi-stage pipeline + scoring observability

[algattik]

Builds on top of PR microsoft#121, and:

• Replaces separate build + release pipelines with a single multi-stage pipeline with stages for Build, Train, ACI, AKS and Webapp deployment.
• ACI, AKS and Webapp deployment are optionally enabled (through Variables).
• Added example of custom traces (logging) and correlating traces with requests with Kusto queries.
• Added example of distributed tracing (client passes a trace header, logged by the scoring service).