Rework span ops for serverless functions

[antonpirker]

Problem Statement

The span ops for serverless functions are not very consistent. See here: https://develop.sentry.dev/sdk/performance/span-operations/#serverless-faas

We should have consistent naming and also look into the GCP ops if we can refactor them to use less similar looking ops.

Solution Brainstorm

Also coordinate with the JS SDK, because they also have serverless functions. So there are the same ops used across SDKs.