Determine standardized template for agenda.md

[kimdhamilton]

As discussed in Working Group training prep session, we want to agree on standardized templates for agenda.md files. Here are the current agenda.md templates.

Note that Working Groups have 1+ work items. They may choose to track agenda.md at the work item level or working group level (we have active instances of each):

• Open Groups
• Working Groups -- if used
• Work items -- if used

Please write any general feedback here or feel free to create PR proposals against individual repos

[kimdhamilton]

Some ideas from TDW's agenda.md