Investigate how to extract cost data from Langfuse

[ErlingHauan]

Description

We should investigate how to use the Langfuse APIs to gather cost data.

There are two use cases:

• Studio wants to fetch all service owner costs in a nightly script
• Studio is currently working on an admin dashboard for service owners, where LLM costs fits naturally

Definition of done

Create two NodeJS scripts:

1. Fetch LLM costs, given arguments fromTimestamp, toTimestamp and serviceOwner
2. Fetch LLM costs for the last 24h, given the argument serviceOwner. This can be a thin wrapper around the first script

These will cover the two use cases and can be implemented in a solution with little change.

[ErlingHauan]

Draft PR: Altinn/altinn-studio#18660