feat(evals): Make context support any type.

[ssbushi]

Update context of EvalInput to be not just strings. This will simplify many JSON parsings and stringifications. Should not affect 3P plugins, since context already has unknown type in BaseEvalDataPoint.

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (manually -- CLI, Dev UI, with and without metrics, with and without custom extractors, on different datatypes)
• Docs to be updated in docs(evals): Updated docs for evals #1512