This engine does no templating; the source text is output exactly
as it was entered into the template engine.
Expose template_dialect to the http injection API and add a test
to show that selecting the Static dialect doesn't perform any
template expansion.
refs: https://github.com/KumoCorp/kumomta/issues/446
If you have a lot of RAM, using only default percentages could
potentially leave some RAM unused. These lua functions
allow more precise control over the limits.