Add a pre-commit hook

Moving my local hooks into a pre-commit hook set that others can find
useful too:
- remove trailing whitespaces and newlines
- don't allow commits to the "main" branch
- python black and python ruff (same args as in the CI)

.pre-commit-config.yaml

@@ -0,0 +1,18 @@
+repos:
+- repo: https://github.com/pre-commit/pre-commit-hooks
+  rev: v2.3.0
+  hooks:
+  - id: end-of-file-fixer
+  - id: trailing-whitespace
+  - id: no-commit-to-branch
+    args: ['--branch', 'main']
+- repo: https://github.com/psf/black
+  rev: 22.10.0
+  hooks:
+  - id: black
+    args: ['--check', '--diff', '.', 'proto/ei-scanner']
+- repo: https://github.com/charliermarsh/ruff-pre-commit
+  rev: v0.0.254
+  hooks:
+  - id: ruff
+    args: ['--ignore=E741,E501', '.', 'proto/ei-scanner']