Redundant specification of snippet path in _config_options.yml

[mahermanns]

Problem

The customization configuration file needs to specify the path it is placed in, which may lead to confusion.

Proposal

Add logic to the customization framework that the snippet variable is automatically inferred from the location of the _custom_options.yml file.

Impact on instructors

Less error-prone customization

Impact on learners

None.

References and Pull Requests