pre-commit: setup pre-commit config to run prettier on YAML files

.pre-commit-config.yaml

@@ -0,0 +1,19 @@
+# pre-commit is a tool to perform a predefined set of tasks manually and/or
+# automatically before git commits are made.
+#
+# Config reference: https://pre-commit.com/#pre-commit-configyaml---top-level
+#
+# Common tasks
+#
+# - Run on all files:   pre-commit run --all-files
+# - Register git hooks: pre-commit install --install-hooks
+#
+repos:
+  # FIXME: Consider adding more, for example by looking at those configured for
+  #        TLJH in https://github.com/jupyterhub/the-littlest-jupyterhub/blob/main/.pre-commit-config.yaml
+
+  # Autoformat: markdown, yaml
+  - repo: https://github.com/pre-commit/mirrors-prettier
+    rev: v2.4.1
+    hooks:
+      - id: prettier

.prettierignore

@@ -0,0 +1,15 @@
+# Helm chart's templates aren't pure YAML files
+**/templates/
+
+# It would be trouble if we had two automatic formatters on the same files. This
+# could happen if we would auto-format the sops generated files with prettier.
+secrets/**/*
+**/secrets.yaml
+!secrets/config/hubs/schema.yaml
+
+# To create a minimal change suggestion, prettier was introduced to auto-format
+# the YAML files only. It is absolutely reasonable to auto-format markdown files
+# and json files as well, but for now, let's make prettier only auto-format
+# YAML.
+**/*.md
+**/*.json