Add pre-commit hook configuration

[wiktorn]

Adding this for those who are forgetful as me, to run terraform fmt or tools/tfdoc.py on changed files.

As of now configuration includes following linters.

• Terraform:
  • terraform fmt
  • terraform tflint
• Python specific:
  • yapf
• Shell scripts
  • shellcheck
  • shfmt
• YAML files:
  • yamllint (disabled as of now)
  • check-yaml
• Other:
  • end-of-file-fixer
  • trailing-whitespace fixer
• Fabric specific
  • tools/tfdoc.py
  • tools/check_boilerplate.py

The checks that are raising most issues in our repo are:

• end-of-file-fixer
• trailing-whitespace fixer
• shellfmt
• shellcheck

Out of those, only shellcheck requires manual fixes, all other 3 above just apply the fix themselves. Shellcheck is controversial so we may want to disable it.

If you want to check the changes the linters introduce run pre-commit run -a to see all effect on the whole repo. When installed, pre-commit hook runs only on changed files in the commit.

---

Checklist

I applicable, I acknowledge that I have:

• Read the contributing guide
• 😁 Ran terraform fmt on all modified files
• 😁 Regenerated the relevant README.md files using tools/tfdoc.py
• Made sure all relevant tests pass