Create/Update the instructions for syncing main branches with upstream

In branching strategy it was decided that we want to be upstream first. As a follow up action, a set of instructions and a template needs to be created/updated for all of the steps involved in syncing main branches of all repos that we manage with upstream/main.

Note: The template should also include how we work with odh-nightlies.

[ ] Template/instructions on syncing the main branches with upstream
[ ] (optional) Diagram how components are inter-related
[ ] Add documentation on connection points with other teams
[ ] Meet with the team and get the feedback on the template/instructions

opendatahub-io / modelmesh-serving

Create/Update the instructions for syncing main branches with upstream #187