🧑‍💻 chore: add options for faster development

Add example:site_core and example:site_core:en_only for faster development

We need development/hugo.toml since the segments still renders images.
See object graph in https://gohugo.io/configuration/segments/

exampleSite/config/development/hugo.toml

@@ -0,0 +1,5 @@
+# Development configuration. Disable this by running: hugo server -e production
+# https://gohugo.io/quick-reference/glossary/#environment
+
+# Exclude folders containing large numbers of images
+ignoreFiles = ['content/guides', 'content/users']