feat(otel): Include opentelemetry-distro[otlp] in the otel extra

[schloerke]

Fixes #2274.

What

Adds opentelemetry-distro[otlp]>=0.45b0 to the shiny[otel] extra, so the standard OpenTelemetry zero-code auto-instrumentation workflow works out of the box:

pip install "shiny[otel]"
opentelemetry-instrument shiny run app.py

• opentelemetry-distro provides the opentelemetry-instrument wrapper and the distro configuration logic that initializes the SDK before app code runs.
• The [otlp] extra supplies the default (OTLP) exporter, and also makes it easy to switch between gRPC and HTTP transports.
• 0.45b0 is the instrumentation release paired with opentelemetry-sdk 1.24.0 (the existing floor), so the lowest-supported-versions CI job resolves cleanly (verified with uv pip compile --python-version 3.10 --resolution lowest-direct --extra theme --extra otel).

Verification

Fresh venv with only this checkout's shiny[otel] installed:

• opentelemetry-instrument --version works, opentelemetry.distro and the OTLP gRPC span exporter import cleanly.
• OTEL_SERVICE_NAME=smoke-test opentelemetry-instrument --traces_exporter console shiny run app.py, then connecting a session, exports session_start, reactive_update, and session_end spans to the console with service.name: smoke-test — no code changes in the app.

Companion

posit-dev/py-shiny-site#380 documents this workflow in the OpenTelemetry Quick Start; it targets the site's rc-shiny-v1.7.0 staging branch, which merges to main when this change is released.

[schloerke]

Superseded by #2349 (merged), which includes the identical pyproject.toml change (opentelemetry-distro[otlp]>=0.45b0 in the shiny[otel] extra) plus the docs/example overhaul making opentelemetry-instrument the documented standard setup. Noting for the record from this PR's verification: the >=0.45b0 floor was confirmed to resolve cleanly in the lowest-supported-versions CI job (uv pip compile --python-version 3.10 --resolution lowest-direct --extra theme --extra otel). The docs companion posit-dev/py-shiny-site#380 targets the site's rc-shiny-v1.7.0 staging branch, which merges to main when the release ships.