Title: Plan to transition to OpenTelemetry

Description: Envoy currently supports OpenTracing (OTr) and OpenCensus (OC) [0]. In May 2019 it was announced that these projects were merging into the new OpenTelemetry (OTel) project [1]. The original plan was to have the legacy project repos moved to read-only by the end of 2019. That hasn't happened but according to the OTel maintainers they are aiming for beta releases in March [2].

Should Envoy:

• keep OTr and OC and add OTel (eventually deprecating the legacy projects)?
• replace OTr and OC with OTel?

#9955 is planning on adding to the OC capability. The OC service / agent repo says its in maintenance mode and points to OTel/opentelemetry-collector

Relevant Links:
0 : config.trace.v3.Tracing.Http
1 : OpenTracing, OpenCensus Merge into a Single New Project, OpenTelemetry
2 : OpenTelemetry Monthly Update: January 2020