Add issue template for new guide proposals

Signed-off-by: Josh Cummings <3627351+jzheaux@users.noreply.github.com>

Author: jzheaux

.github/ISSUE_TEMPLATE/new-guide-proposal.md

@@ -0,0 +1,23 @@
+---
+name: New Guide Proposal
+about: Suggest a new getting started guide
+title: "Guide: "
+labels: guide-proposal
+assignees: ''
+---
+
+## 💡 Thanks for the idea!
+
+Thank you for taking the time to propose a new guide — community ideas help make Spring Guides more useful for everyone.
+
+---
+
+## 📌 Proposed Title
+
+<!-- What would you call this guide? e.g. "Getting Started with Spring Batch" -->
+
+## 📝 Brief Description
+
+<!-- In a few sentences, what will someone learn from this guide?
+     What problem does it solve, or what concept does it introduce? -->
+