RUM: sourcemap.error on and sourcemap.updated are set overzealously

[axw]

We currently store sourcemap.error and sourcemap.updated on every stack frame in RUM spans and errors if no matching sourcemaps have been uploaded. This will bloat documents considerably. I would like to revisit this decision, and only set these fields under certain conditions. Specifically:

• Only set sourcemap.error if a matching sourcemap is found and some error occurred while attempting to match and update frames. Not matching a sourcemap to a frame is not an error. For now we'll continue to set sourcemap.error at the per-frame level, but later it might make sense to set at the document level when performing sourcemapping in ingest node -- this would be more natural since we can use an on_failure handler.
• Only set sourcemap.updated (to true) when a frame is matched and updated. Non-presence of this field means the frame has not been updated.