fix(terraform_docs): Restore --hook-config=--add-to-existing-file default behavior. Regression from 1.94.0.

[MaxymVlasov]

Put an x into the box if that apply:

• This PR introduces breaking change.
• This PR fixes a bug.
• This PR adds new functionality.
• This PR enhances existing functionality.

Description of your changes

Fixes #715

How can we test changes

broken:

testdir=$(mktemp -d)
cd $testdir
touch main.tf README.md
echo "
repos:
  - repo: https://github.com/antonbabenko/pre-commit-terraform
    rev: v1.94.2 # issue introduced in 1.94.0
    hooks:
      - id: terraform_docs
" > .pre-commit-config.yaml
git init
git add -A
pre-commit run

fixed:

testdir=$(mktemp -d)
cd $testdir
touch main.tf README.md
echo "
repos:
  - repo: https://github.com/antonbabenko/pre-commit-terraform
    rev: c0b1f38bae3b34f3f223bc73a8b384e2e7a766d7
    hooks:
      - id: terraform_docs
" > .pre-commit-config.yaml
git init
git add -A
pre-commit run

testdir=$(mktemp -d)
cd $testdir
touch main.tf README.md
echo "
repos:
  - repo: https://github.com/antonbabenko/pre-commit-terraform
    rev: c0b1f38bae3b34f3f223bc73a8b384e2e7a766d7
    hooks:
      - id: terraform_docs
        args:
        - --hook-config=--add-to-existing-file=true
" > .pre-commit-config.yaml
git init
git add -A
pre-commit run

[antonbabenko]

This PR is included in version 1.94.3 🎉