Add config linting script that checks for bool casing (#6203)

Add a linting script that enforces all boolean values in the default config be lowercase.

This has annoyed me for a while so I decided to fix it.

scripts-dev/config-lint.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+# Find linting errors in Synapse's default config file.
+# Exits with 0 if there are no problems, or another code otherwise.
+
+# Fix non-lowercase true/false values
+sed -i -E "s/: +True/: true/g; s/: +False/: false/g;" docs/sample_config.yaml
+
+# Check if anything changed
+git diff --exit-code docs/sample_config.yaml

scripts-dev/lint.sh

@@ -10,3 +10,4 @@ set -e
 isort -y -rc synapse tests scripts-dev scripts
 flake8 synapse tests
 python3 -m black synapse tests scripts-dev scripts
+./scripts-dev/config-lint.sh