Inverted logic in configuration merge

[schroedingersZombie]

In sydent/config/init.py is an inversion of logic.
In line 229 and following, the default config is populated into the config object. The comment indicates, that if a config file exists, all default configs should go into the DEFAULT section. With the current logic all default values go into their specific sections, when the config file exists, overriding all DEFAULT section settings made in the config file.
This same bug also causes the generated config file to have (almost) all options in the DEFAULT section.

The fix is to remove the "not" in line 229, as I've done in my fork https://github.com/matrix-org/sydent/compare/main...schroedingersZombie:fix-inverted-config-merge?expand=1

Unfortunately Matrix Organisations Contribution Guidelines are (possibly unintentionally) transphobic. As I will not give my legal name, I'm barred from contributing code.