Add option to define refs in issue templates (#17842)

Adds a markdown header option `ref` that allows you to set the ref the issue should belong.

docs/content/doc/usage/issue-pull-request-templates.en-us.md

@@ -69,6 +69,7 @@ Inside the directory can be multiple issue templates with the form
 name: "Template Name"
 about: "This template is for testing!"
 title: "[TEST] "
+ref: "main"
 labels:
 
 - bug
@@ -82,4 +83,4 @@ This is the template!
 In the above example, when a user is presented with the list of issues they can submit, this would show as `Template Name` with the description
 `This template is for testing!`. When submitting an issue with the above example, the issue title would be pre-populated with
 `[TEST] ` while the issue body would be pre-populated with `This is the template!`. The issue would also be assigned two labels,
-`bug` and `help needed`.
+`bug` and `help needed`, and the issue will have a reference to `main`.