Move workflow to its own database/api

[antho1404]

Dependency #1201

There is a lot of copy/paste from the existing service SDK/API. I didn't change the workflow engine, just moved it from workflow to engine package

• package workflow with the definition
• remove workflows from services
• create protobuf type
• create workflow SDK
• create workflow API
• update the workflow engine to use workflow SDK.

Now there is 4 new apis:

• Workflow.Create
• Workflow.Delete
• Workflow.Get
• Workflow.List

When we create the workflow, all the instances will be validated and once recorded in the database the workflow engine will start to process executions related to this workflow.
There is no need to deploy a service with no source code.

[krhubert]

Why you want to move workflow package to the engine. It's rather a general name and also the name of main repo.

[antho1404]

Why you want to move workflow package to the engine. It's rather a general name and also the name of main repo.

We have now a model called workflow and the workflow engine that is connecting the workflow definition to the executions so this cannot be in the same package.

We could go with workflow_engine but https://blog.golang.org/package-names.

I'm open for suggestions on the name for this package or just keep it as it is

[NicolasMahe]

Why you want to move workflow package to the engine. It's rather a general name and also the name of main repo.

We have now a model called workflow and the workflow engine that is connecting the workflow definition to the executions so this cannot be in the same package.

We could go with workflow_engine but https://blog.golang.org/package-names.

I'm open for suggestions on the name for this package or just keep it as it is

let's keep it like this for this PR and change it in a future PR.
I suggest to group all workflow stuff in one folder with multiple subpackage (lib approach):

workflow
|  types
|  engine
|  ....

[antho1404]

Another PR created for the renaming #1208
Let's validate/merge this one if it's ok and discuss on the other PR

[krhubert]

@antho1404 just to remind you you can use "github.com/golang/protobuf/jsonpb" package to do conversion the same way as for pbstruct. Not necessary in this pr