[Sequence diagram] Create participant in box

[tsnobip]

Proposal

In sequence diagrams, it's now possible to add participants to boxes, but not when they're created later in the sequence diagram.

It'd be convenient to have a syntax to create a participant and place it in a box with the following syntax:

create participant $PARTICIPANT_NAME [as $ALIAS] in $BOX_NAME

Example

sequeneceDiagram
  box Agency
  participant PM as Project manager
  end
  create participant GD as Graphic Designer in Agency
  PM->>GD: hires in the agency

Screenshots

No response

[pohly]

Also relevant here is the ordering. At the moment, the following creates the new "proxy" participant to the very far right:

sequenceDiagram
    participant apiserver
    box kubelet
      participant plugins as plugin manager
      participant manager as DRA manager
    end
    box DRA driver plugin
       participant grpc as gRPC servers
    end
    Note right of grpc: handles registration socket and plugin socket
    plugins -->> grpc: pluginregistration.Registration/GetInfo
    grpc -->> plugins: GetInfo response: PluginInfo{Type:DRAPlugin}
    plugins -->> grpc: pluginregistration.Registration/NotifyRegistrationStatus
    grpc -->> plugins: 
    plugins ->> manager: add plugin
    loop while plugin is registered
       manager -->> grpc: v1alpha1.REST/NodeObject{Name, UID}
       grpc -->> manager: 
       create participant proxy as REST proxy
       manager ->> proxy: start
       proxy -->> grpc: v1alpha1.REST/Proxy
       destroy proxy
    end

I want it in the "kubelet" box before "grpc".

I am working around this by pretending that "proxy" exists from the beginning and merely gets activated, which is not quite right.