doc: add comment on method to set savepoint_limit dynamically savepoint_limit isn't a real config option as in config.ini. I generate one on the fly for use in the backend during import. While this is arguably a valid config option, it is also something that is niche (import a tracker to postgres) and adds clutter to config.ini.

[run]

# ignore the dist utils. They are not part of the code base
# we are going to test. They are used by maintainers only.
omit = roundup/dist/*