Fully integrate the SDKs into FIT

See CBD-5053 for details.

Note that Python is a special case as there is an early, prototype version of the performer written by Charlie Hayes here https://github.com/couchbaselabs/perf-sdk/tree/main/performers/python

However, it will need some major TLC to update it for FIT:

• Migrating into FIT (transactions-fit-performers).
• Improve the results streaming, as this performer has a naive one-at-a-time approach that won't scale.  See the GRPC documentation and the other performers for examples.
• Migrate to the current GRPC, which is much advanced beyond the early prototype GRPC this performer was built against.

Honestly the code is so minimal that it's probably easiest to start afresh and only use parts of the existing code for inspiration (e.g. the Dockerfile is probably still useful).  It'll likely take more time to figure out what's changed, than just writing a new one from scratch based on the GRPC documentation and other performers.