[Feature Request]: Backfill HttpEvents from cached PerformanceResourceTiming with initiator types Fetch, Xhr, and Beacon

[williazz]

Please provide your feature request

RUM can records HTTP requests in two formats:

1. As an HTTP event with status codes and nested objects for request/response
2. As a ResourceEvent, which includes full latency breakdown. But no status code or nested object for request/response

There is a gap in RUM's capabilities, however, because (2) can be recorded from the PerformanceAPI cache even if RUM is initialized much later. But (1) can only be recorded at runtime. Instead, RUM should backfill cached PerformanceResourceTiming entries into HttpEvents when HTTP Requests are sent by Fetch, Xhr, and Beacon.

The reason we should do this is because

1. PerformanceResourceTiming.responseStatus has received broader browser support and should be used in production wherever possible. https://developer.mozilla.org/en-US/docs/Web/API/PerformanceResourceTiming/responseStatus
2. Prevent data loss

[Optional] Nice to haves to complete the story

1. There should be a way to link the ResourceEvent and HttpEvents for the same HTTP requests
2. There should be a way to observe all beacon requests

[williazz]

[Optional]

3. Add responseStatus to ResourceEvent schema, since it is no longer an experimental feature.

[sonu-gameskraft]

Core functionality of RUM for SSR website is not working to capture http error.

1. Upgraded the RUM version from 1.18.0 to 1.19.0
2. I would like to clarify that the Performance API focuses on performance-related metrics, which don't meet my request. I only want to track HTTP and error metrics. But still, I tried implementing the script you suggested for the Performance API, but unable to catch the 403 error.
3. I've increased the priority of the cwr.js file, so now it's loaded before the generated JS file. However, we are still experiencing issues with session and not catching HTTP errors.
4. performance telemetry also not able to capture 4xx and 5XX error