Update issues template: Add Agenda Plus template

Add an agenda+ template so participants can add issues to the agenda even if they can't apply labels themselves.

.github/ISSUE_TEMPLATE/agenda-item-template.md

@@ -0,0 +1,16 @@
+---
+name: Agenda Item template
+about: Use this template to add an item to the next meeting's agenda
+title: 'Agenda Request -  '
+labels: agenda+
+assignees: AramZS, seanturner
+
+---
+
+## Agenda+: What do you want to discuss?
+
+Add a title above that describes in a little more detail the topic for discussion. In short clear sentences please describe here what you would like to make the focus of this discussion. When writing this section include what goals you have for the outcome.
+
+### Links
+
+If your agenda item wishes to discuss some external document, spec, or proposal, you should include links to that document here. Please do not assume a reader has read any existing document. Always link.