Add script to preview release notes (#5620)

Add a script to preview the release notes that would be generated if we
were to create a release now.

scripts/preview_release_notes.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+# Preview the release notes that would be generated if we were to create a
+# release now.
+
+gh api -X POST /repos/jesseduffield/lazygit/releases/generate-notes \
+  -f tag_name=v0.99.0 \
+  -f target_commitish=master \
+  -q .body | code -