Enable HTTP caching by default, and disable it conditionally.

Review Request #13040 — Created May 11, 2023 and submitted — Latest diff uploaded




RBTools's HTTP caching is conditional based on the version of Review
Board. In versions prior to 2.0.14, caching was broken in various ways,
so RBTools only enables it if the root resource claims a newer version.
By default, though, caching was disabled, meaning the root resource
never went through the caching support.

Since most companies are using versions far newer than the minimum of
2.0.14, this change flips the logic around. Caching is now enabled by
default for all resources, and is then disabled if the root resource
claims an earlier version. This gives us the best performance available
for most users.

Some API transport and response testing infrastructure had to be updated
to test the new code paths. Those are included in this change.

Unit tests pass.

Tested posting changes against reviews.reviewboard.org and local