[CI][TEST] update pre-commit hooks and use pre-commit for style tests in CI (#1409)

Ref issue:

- #1408

Changes:

- Add `.editorconfig`
- Add `pre-commit-hooks`:

    ```yaml
    - repo: https://github.com/pre-commit/pre-commit-hooks
      rev: v4.4.0
      hooks:
        - id: check-symlinks
        - id: destroyed-symlinks
        - id: trailing-whitespace
        - id: end-of-file-fixer
        - id: check-yaml
        - id: check-toml
        - id: check-ast
        - id: check-added-large-files
        - id: check-merge-conflict
        - id: check-executables-have-shebangs
        - id: check-shebang-scripts-are-executable
        - id: detect-private-key
        - id: debug-statements
    ```
- Add `flake8` to `pre-commit` config and add `.flake8` file
- Use `pre-commit` for style tests in CI
- Run `pre-commit` and fix existing violations:
    - fix trailing spaces
    - fix end-of-files
    - fix mod file mode with `chmod -x`
    - run `autopep8` on existing code
    - fix `flake8` violations

docs/getting-started/installation.rst

@@ -17,7 +17,7 @@ Binary wheels are available for CPython 3.6-3.9 and PyPy 3.6-3.7.
 And the latest nightly release:
 
 .. code-block:: bash
-  
+
       pip install -U --pre triton
 
 
@@ -50,6 +50,6 @@ You can then test your installation by running the unit tests:
 and the benchmarks
 
 .. code-block:: bash
-      
+
       cd bench
       python -m run --with-plots --result-dir /tmp/triton-bench