Add checkbox to PR checklist for experimental feature use (PowerShell#9619)

Author: KirkMunro

.github/PULL_REQUEST_TEMPLATE.md

@@ -13,10 +13,14 @@
 - [ ] [PR has a meaningful title](https://github.com/PowerShell/PowerShell/blob/master/.github/CONTRIBUTING.md#pull-request---submission)
     - Use the present tense and imperative mood when describing your changes
 - [ ] [Summarized changes](https://github.com/PowerShell/PowerShell/blob/master/.github/CONTRIBUTING.md#pull-request---submission)
-- [ ] [Change is not breaking](https://github.com/PowerShell/PowerShell/blob/master/.github/CONTRIBUTING.md#making-breaking-changes)
 - [ ] [Make sure all `.h`, `.cpp`, `.cs`, `.ps1` and `.psm1` files have the correct copyright header](https://github.com/PowerShell/PowerShell/blob/master/.github/CONTRIBUTING.md#pull-request---submission)
 - [ ] This PR is ready to merge and is not [Work in Progress](https://github.com/PowerShell/PowerShell/blob/master/.github/CONTRIBUTING.md#pull-request---work-in-progress).
     - If the PR is work in progress, please add the prefix `WIP:` or `[ WIP ]` to the beginning of the title (the `WIP` bot will keep its status check at `Pending` while the prefix is present) and remove the prefix when the PR is ready.
+- **[Breaking changes](https://github.com/PowerShell/PowerShell/blob/master/.github/CONTRIBUTING.md#making-breaking-changes)**
+    - [ ] None
+    - **OR**
+    - [ ] [Experimental feature(s) needed](https://github.com/MicrosoftDocs/PowerShell-Docs/blob/staging/reference/6/Microsoft.PowerShell.Core/About/about_Experimental_Features.md)
+        - [ ] Experimental feature name(s): <!-- Experimental feature name(s) here -->
 - **User-facing changes**
     - [ ] Not Applicable
     - **OR**