Normalize http.response.status_code for Metrics & Alerts

[smeubank]

Background:
http.status is set in different places in different SDKs which creates some problems in processing for metrics extraction and then

https://www.notion.so/sentry/Expand-Metrics-for-Alerts-cdfa32d7624e498b8246c3f131f753f1#17480955e2fb4407b619b9236bc2723a

Requirements:
Need status code number (standard HTTP status code 2xx, 4xx, 5xx, etc)
The SDK should never on it's own set this as a tag - as this adds expense due to indexing being based on tags
the location of storage needs to be in a standard location based on span schema
follow existing standard in develop docs
Starfish has a workstream to standardize span schema getsentry/rfcs#89

[antonpirker]

UPDATE: The span data fields should be called http.response.status_code. See: https://develop.sentry.dev/sdk/performance/span-data-conventions/#http