[Backport 12.4] [TASK] Add .ddev/.gitignore file (#480)

The .ddev/.gitignore file is created when configuring a new project.
But it also ignores itself (`/.gitignore`), so this one is commented out.
Using this .gitignore is cleaner as it takes possible custom commands
and configuration into account.

Releases: main, 12.4

---------

Co-authored-by: Chris Müller <[email protected]>

.ddev/.gitignore

@@ -0,0 +1,41 @@
+#ddev-generated: Automatically generated ddev .gitignore.
+# You can remove the above line if you want to edit and maintain this file yourself.
+/.gitignore
+
+/**/*.example
+/.dbimageBuild
+/.dbimageExtra
+/.ddev-docker-*.yaml
+/.*downloads
+/.global_commands
+/.homeadditions
+/.importdb*
+/.sshimageBuild
+/.venv
+/.webimageBuild
+/.webimageExtra
+/apache/apache-site.conf
+/commands/.gitattributes
+/commands/db/mysql
+/commands/host/launch
+/commands/web/xdebug
+/commands/web/live
+/config.local.y*ml
+/db_snapshots
+/import-db
+/import.yaml
+/mutagen/mutagen.yml
+/mutagen/.start-synced
+/nginx_full/nginx-site.conf
+/postgres/postgresql.conf
+/providers/acquia.yaml
+/providers/lagoon.yaml
+/providers/platform.yaml
+/providers/upsun.yaml
+/sequelpro.spf
+/settings/settings.ddev.py
+/traefik/config/ddev-test.yaml
+/traefik/certs/ddev-test.crt
+/traefik/certs/ddev-test.key
+/xhprof/xhprof_prepend.php
+/**/README.*