Allow Keyword match with filename for custom detectors

[vexvec]

Description

Currently a custom detector needs at least 1 keyword defined. The detector is only executed if the keyword appears in the text. This is usually enough for most cases.
For custom detectors it would be a benefit if the detector would be executed if the keyword appears in the filename (full path) to make it possible to detect secrets that use a complete file and where there is no uniq keyword within the text that can be used to identify it.

Preferred Solution

Introduce an additional config option (keyword_in_filename) for custom detectors to enable that keywords are also checked against the filename.

Additional Context

References

[kashifkhan0771]

I discussed this with the team internally, and we agree it's an interesting feature to implement. We'll consider it for the future potentially not just for custom detector, but for all detectors.