tracing: otel multitenant support

[paul-r-gall]

Commit Message: Add Multitenancy support for the OpenTelemetry Tracer.
Additional Description: Allow different OpenTelemetry resources to be associated with different Routes or Streams, addressing Multitenancy requirements.

1. ResourceProvider and ResourceDetector have an additional method which can get/detect a resource based on StreamInfo.
2. The Tracer now carries a shared_ptr to the ResourceProvider. This resource provider is invoked on span initialization in order to deduce the resource. There is no way (yet) to change the resource mid-span.
3. Child spans always have the same Resource as parent spans.
4. Tracer maintains a per_tenant_span_buffer_ to group spans by Resource ptr. We group by pointer in order to avoid copies and complicated hashing.

Risk Level: Low
Testing: Unit, Integration
Docs Changes: upcoming commit
Release Notes: upcoming commit

[repokitteh-read-only]

CC @envoyproxy/api-shepherds: Your approval is needed for changes made to (api/envoy/|docs/root/api-docs/).
envoyproxy/api-shepherds assignee is @markdroth
CC @envoyproxy/api-watchers: FYI only for changes made to (api/envoy/|docs/root/api-docs/).

🐱

Caused by: #43554 was opened by paul-r-gall.

see: more, trace.

[paul-r-gall]

Relevant to #43184

[mathetake]

unnecessary change