Improve identification of binaries

[agateau-gg]

Environment

• ggshield version: 1.23.0
• Operating system (Linux, macOS, Windows): Linux
• Operating system version: Ubuntu 22.04
• Python version: Python 3.10

Describe the bug

When iterating on a directory or a Docker image, ggshield often hits binaries, like executable files. We should not try to scan these files by default, at least until #396 is done.

Steps to reproduce:

1. Scan a directory containing binaries, such as /usr/bin on a Unix system (ggshield secret scan path -ry /usr/bin)
2. Notice ggshield tries to detect the encoding of the files

Expected result:

ggshield should silently skip binary files.