Update MP 6.0 to clarify MP OpenTracing and MP Telemetry relationship

[Emily-Jiang]

MP 6.0 will remove MP OpenTracing and add MP Telemetry. In this spec, the future direction of both specs should be clearly speced, such as
MP OpenTracing will no longer in active development and are deprecated. The future is MP Telemetry. All applications that use MP OpenTracing should be migrated to MP Telemetry.
Bruno and Jan are creating blogs to document some migration routes to cover this space. MP umbrella spec should add the link to the blogs in due course.