build SDK releases from master

[turadg]

What is the Problem Being Solved?

Currently we have a branch for each release of SDK. E.g.

• https://github.com/Agoric/agoric-sdk/tree/dev-upgrade-13
• https://github.com/Agoric/agoric-sdk/tree/dev-upgrade-14
• https://github.com/Agoric/agoric-sdk/tree/dev-upgrade-15

This approach requires painstaking cherry picking and has been the source of some confusion.

Description of the Design

Make it safe to cut releases from master. This will require at least,

### Tasks
- [ ] #8961 
- [ ] #8219 
- [ ] upgrade all vats
- [ ] https://github.com/Agoric/agoric-sdk/issues/9417

Security Considerations

Scaling Considerations

Test Plan

Upgrade Considerations

[Chris-Hibbert]

In Slack, @mhofman said

the prerequisite to releasing from master is roughly that all vats are upgradable and upgraded, or that the code for non upgradable vats is functionally equivalent in master