feat: update OrchestrationDefinition API model

[paullatzelsperger]

This PR changes the data model of the orchestration definition API by:

• introducing the OrchestrationTemplate: OrchestrationDefinition objects are generated based off of that template and linked to it with the templateRef property
• added a get-by-templateref endpoint which allows to look for all OrchestrationDefinitions that were generated on a certain template.

[jimmarino]

Can we get rid of the Stream abstraction and use Seq/Seq2 instead? The Stream abstraction isn't needed, and any required filtering/transformation can be done using composable Seq/Seq2 in a range using functions:

for n := range MapBar(FilterFoo(getResults())) {
    // Do something
}

The approach is used in the memory and SQL stores. Any general functions (if they are needed) can go into common/collections but I'm not sure if such functions are neded.