chore: sync rapidjson to upstream

We drop the pow of 2 allocation change, because the increased
number of realloc(3) has little impact on performance, but give
us chances to *not* move the data for the last realloc.
feat(bundle): make capacity configurable

bundle: default to 5MB, configurable
unmanaged_bundle: fixed to 5MB
managed_bundle: no default, configurable

Increase managed_bundle size for demo to 15MB.
fix(demo): stop restricting assign blocks payload

Each file needs at least 1 assign blocks request, each request
theoretically cannot go beyond 58K.