[Feature Request] Implicit gradient support

[Benjamin-eecs]

Motivation

for imaml and model-based meta-rl algos

Solution

• [x] linear system solver for hessian vector product
• [x] jaxopt decorator
• [ ] imaml example
• [x] implicit differentiation tutorial
• [x] api docs
• [ ] readme

Checklist

• [x] I have checked that there is no similar issue in the repo (required)