web: integrate OpenTelemetry client observability packages

Created by: valerybugakov

Context

Add basic configuration of the OpenTelemetry tracing to the web application. Based on prior work. Honeycomb guide.

Changes

1. Removed ENABLE_MONITORING env variable in favor of ENABLE_SENTRY and ENABLE_OPEN_TELEMETRY. Required for standalone-web-server in the development environment to avoid accidentally sending telemetry data from the local env.

2. Integrated @opentelemetry packages and moved them into a separate chunk. Added new script tags required for the new initial chunk.

   

3. Enabled @opentelemetry/instrumentation-fetch.

   

Note: we won't be collecting data until the backend tunnel PR is merged.

Closes https://github.com/sourcegraph/sourcegraph/issues/39273 Closes https://github.com/sourcegraph/sourcegraph/issues/39281

Test plan

1. Checkout to https://github.com/sourcegraph/sourcegraph/pull/39453
2. Set dev-private site config to use opentelemetry
3. Set observability.client in the site config.
4. sg start otel
5. sg start
6. Open a web page with API requests.
7. See traces logged to Jaeger.