Add possibility to run diffyscan against the specified project folder

[folkyatina]

Seems like we need to run diffyscan in some dir where the config.json located and where digest will be stored as well.

Something like this:
PROJECT_DIR=/someproject/ python main.py

Also, there is a possibility to extract github repo path from git in the project dir

[tamtamchik]

Partially addressed: diffyscan now accepts a directory of configs (positional path → iterates *.json/*.yaml/*.yml in the folder, diffyscan/diffyscan.py), and falls back to config.{json,yaml,yml} in the CWD. The remaining part of this request — inferring the GitHub repo/commit from git in the project dir — is not implemented; the repo is still read from github_repo in the config.