doc: Insert Arista license header in all source files

[carlbuchmann]

Change Summary

Insert license header in all source files

Proposed changes

Add pre-commit hook to insert license headers in:

• Python files
• Documentation files

Increase the scope of pre-commit hooks to include ./docs

The following files had additional fixes from pre-commit hooks

trim trailing whitespace.......................................................Failed
- hook id: trailing-whitespace
- exit code: 1
- files were modified by this hook

Fixing docs/advanced_usages/as-python-lib.md
Fixing docs/cli/get-inventory-information.md
Fixing docs/getting-started.md
Fixing docs/cli/debug.md

fix end of files...............................................................Failed
- hook id: end-of-file-fixer
- exit code: 1
- files were modified by this hook

Fixing docs/imgs/animated-svg.md
Fixing docs/snippets/anta_help.txt
Fixing docs/api/tests.system.md
Fixing docs/imgs/anta-nrfu.svg
Fixing docs/api/tests.md
Fixing docs/faq.md
Fixing docs/imgs/anta-nrfu.cast

[titom73]

LGTM! Thank you