notebooks: clean compute block JSON inputs

Created by: rvantonder

Stacked on https://github.com/sourcegraph/sourcegraph/pull/32626

Just finesses some JSON handling of the compute data we persist and gets rid of a lint disable. Basically, it helps a bit with by making experimental features optional to preempt that annoying issue where we can't ever remove and clean up fields in a schema because an app expects it to exist.

Test plan

Manual testing of experimental feature