feat(otel): add OpenTelemetry SpanProcessor, Propagator, Extractor (#779)

* feat(otel): add OpenTelemetry SpanProcessor, Propagator, Extractor

* update

* set kind on transaction as well

* replace unknown span op with empty string

* replace empty op with description

* try serializing tests

* on test init, close existing client if any

* remove useless line

* address comments

* simplify logic and capture span attributes

* fix tests

* restructure tests

* clippy

* Update shared.rs

* Update shared.rs

* address comments

* move comment

* nit

* fix test warnings

Author: lcian