A72 update: various clarifications and corrections

[yashykt]

Changes -

• Add link to OpenCensus's binary format for grpc-trace-bin
• Add names for parent call span, attempt span and server span based on existing OpenCensus implementation.
• Clarify previous-rpc-attempts does not include transparent retries as per https://github.com/grpc/proposal/blob/master/A45-retry-stats.md
• Add missing sequence-number attribute from events in examples.
• Remove superfluous and confusing sent and received words from Inbound message received and Outbound message sent. Reasoning - Inbound and Outbound already convey the direction. The way it is currently structured, you could have Outbound message sent followed by Outbound message compressed , and Inbound compressed message followed by Inbound message received. In the future, we might want additional events (especially for C++) for when we know that bytes have actually been sent on the wire.

[yashykt]

cc @markdroth @dfawley

[YifeiZhuang]

LGTM