[Starfish] Add starfish v1 attribute `http.request.method` to span data

### Description

### Project Board

https://github.com/orgs/getsentry/projects/150/views/1

### Description

See https://github.com/getsentry/team-sdks/issues/20
Add a new field to the span data field, http.request.method, representing the http method (GET, POST, PUT).