requirements.txt: Generate package lock file

- Use pip-tools' pip-compile command via '.venv/bin/pip-compile'
- Note: For pip-compile to work for this project we have to add:
```
[tool.setuptools]
py-modules = []
```
  Details here:
  - jazzband/pip-tools#1711 (comment)
  - pypa/setuptools#3197 (comment)

pyproject.toml

@@ -10,10 +10,15 @@ dev = [
   "black",
   "isort",
   "ruff",
+
+  "pip-tools",
 ]
 
 [tool.black]
 skip-string-normalization = true
 
 [tool.isort]
 profile = "black"
+
+[tool.setuptools]
+py-modules = []

requirements.txt

@@ -0,0 +1,12 @@
+#
+# This file is autogenerated by pip-compile with Python 3.11
+# by the following command:
+#
+#    pip-compile
+#
+asgiref==3.6.0
+    # via django
+django==4.2.1
+    # via mypythondjangoproject (pyproject.toml)
+sqlparse==0.4.4
+    # via django