Add pre-commit-config file

Adds a precommit config file (and .flake8 config) to enable
CI in jazzband organization. Adds basic following checks:
 * Black
 * isort
 * flake8
 * end-of-file-fixer
 * trailing-whitespace

.flake8

@@ -2,4 +2,4 @@
 max-line-length = 88
 extend-ignore = E203
 per-file-ignores=
-    test_dj_database_url.py: E501, E265
+    test_dj_database_url.py: E501, E265

.pre-commit-config.yaml

@@ -0,0 +1,23 @@
+repos:
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v4.0.1
+    hooks:
+      - id: end-of-file-fixer
+      - id: trailing-whitespace
+
+  - repo: https://github.com/pycqa/isort
+    rev: "5.10.1"
+    hooks:
+        - id: isort
+          args: ["--profile", "black"]
+
+  - repo: https://github.com/psf/black
+    rev: 22.3.0
+    hooks:
+      - id: black
+        args: [--target-version=py38]
+
+  - repo: https://github.com/pycqa/flake8
+    rev: '4.0.1'
+    hooks:
+      - id: flake8