Document how to control simulation parameters

[Jondolf]

What problem does this solve or what need does it fill?

Simulation details like the timestep, solver iteration count, "slop" (allowed penetration), damping, and so on can be modified using the IntegrationParameters configuration. It is briefly mentioned in the "Simulation structures" section of the core Rapier docs, but it essentially just points to API docs, which doesn't really cover how the parameters can be accessed or modified. The descriptions of the properties are also rather brief and often not very user-friendly (What are PGS iterations? Or islands? How do CCD substeps differ from solver iterations?).

In addition, the docs for the Bevy plugin and JS bindings don't mention the integration parameters at all, and the way they are accessed is different from the core Rapier. For example, in the Bevy plugin, they are in the RapierContext resource (which is also not on the website except for the spatial query sections).

What solution would you like?

It would be very useful to have these kinds of simulation configuration options documented. It should cover how they can be accessed and modified, and how the most important options (like the timestep and solver iteration count) affect the simulation. These docs should exist for the Bevy plugin and JS bindings in addition to the core Rapier.