feature: Support for River models in BentoML

[jsamanta]

Feature request

We have been developing and experimenting river (https://riverml.xyz/latest/api/overview/) for training and inferencing time series and continuous machine learning tasks and would like to add support for river in BentoML.

We have also created a custom python module to add river models using MLflow which can be saved in the BentoML model's repository and later can be retrieved from the BentoML for inferencing.

Motivation

River offers a diverse selection of ML models for online learning that are much more efficient than the sklearn models, and integrating this MLflow would create a comprehensive ML solution.

Other

I would love to contribute the code that I've created and would like to submit a PR, but I'd appreciate it if you could put me in the right direction.