[Enhancement] Add option to exclude .gitignore-ed files

As a developer and user of shhgit scanning local directories I most likely will have local files like for example .env files containing secrets which are protected through the full-disk-encryption of my machine and prevented to be accidentally committed through the .gitignore or ~/.gitignore_global file.

Expected behavior:

• I can specify an option to exclude those files matching gitignore-entries from the search

Actual behavior:

• I have to filter those entries from the shhgit log after the scan finished

Though this option should not be enabled by default as it reduces the visibility of secrets lingering around on the disk (which shouldn't exist in the first place) which could be committed through git add -f…