[BUG] container missing from multi-essence Flows in v8.2 #240

Describe the bug
In TAMS v8.2 multi-essence Flows no longer have a container property, however it is possible to add segments to a multi-essence Flow

Thanks to @danjhd for the initial report

Expected behavior
container, codec et al are retained as in v8.1

Suggested fix
Add the missing flow-technical.json schema

Additional context
This was a regression introduced by #130