Patching of services (aka Jackish branching)

[tillrohrmann]

In case that people have not properly versioned their services, forgotten to register error-defer handlers or otherwise gotten themselves into a situation where they need to change their service code while keeping already started invocations working, we can offer a patching API that allows to introduce branches for the different patch versions. This is similar to https://legacy-documentation-sdks.temporal.io/typescript/patching.

The patching API can be implemented as an SDK concept only by using custom journal entries.

[tillrohrmann]

The patching of services is described in this google doc.

[slinkydeveloper]

I moved this here as it affects the whole system semantics.