[STAR-3422] Consolidate and improve templates for epic updates

Also:

• Update scope of epic planning role to include checking epic updates for info about ongoing and future work.
• Change deadline for posting epic updates, to give epic owners a chance to take their time and do it more calmly.
• Update definition of epic owner role with some additional details/pointers about scheduling as well as budget and progress tracking.
• Explicitly document division of responsibilities for budget tracking.
• Move new epic update template from List of roles page to page on Epic Management.

Tickets

Documentation updates

• STAR-3422

Reviews

• SE-6109
• FAL-3587
• BB-8341
• STAR-3423
• MNG-4039

... and corresponding subtasks.

Testing

• Confirm that formatting looks correct in rendered version of changes.