[OC-5477] Improve epic update template.

Part of cell support initiative to improve processes around capacity planning and sustainability management.

Also includes some changes that may help client/epic owners with certain aspects of project management (ref, ref).

Tickets

• OC-5477

Related work

• Project Management Guidelines

Testing

For rendered versions of the new epic update templates see the comments section of OC-5477.

Reviewers

• @gabrieldamours