* caddytls: Make on-demand 'ask' permission modular
This makes the 'ask' endpoint a module, which means that developers can
write custom plugins for granting permission for on-demand certificates.
Kicking myself that we didn't do it this way at the beginning, but who coulda known...
* Lint
* Error on conflicting config
* Fix bad merge
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Co-authored-by: Francis Lavoie <lavofr@gmail.com>