[1.16] Dapr Agents OpenTelemetry with Phoenix Integration Docs

[sicoyle]

What content needs to be created or modified? Recently, we added OpenTelemetry support with Phoenix Integration to Dapr Agents: https://github.com/dapr/dapr-agents/pull/168

This is a super great addition to the project that users will benefit from reading up on our OpenTelemetry support in Dapr Agents, showcasing the in-depth tracing feature that was added.

Describe the solution you'd like Currently, the Dapr Agents docs fall under daprdocs/content/en/developing-applications/dapr-agents/.

The solution we want is for OpenTelemetry and tracing information to be easy to find in the Dapr Agents Documentation and has a section dedicated to dapr-agents-observability.md or something along those lines.

It can include the Phoenix UI pictures for reference too as they look great, and are another open source project.

Where should the new material be placed? Somewhere under daprdocs/content/en/developing-applications/dapr-agents/. Maybe a dapr-agents-observability.md file or something along those lines.

A little section under "Why Dapr Agents" would be great too to highlight this feature.

The associated pull request from dapr/dapr, dapr/components-contrib, or other Dapr code repos https://github.com/dapr/dapr-agents/pull/168

Additional context Currently the Dapr Agents docs are in the 1.16 preview https://v1-16.docs.dapr.io/developing-applications/dapr-agents/