Enable multiple actions per Pipeline Stage

### Epic

_No response_

### Description

**As a:** FlowFuse User

**I want to:** be able to add multiple actions to a single stage of a Pipeline

**So that:** I can easily push flows to a small set of Instances, rather than having to make Groups for every variation I want.

This will also then enable future Pipeline enhancements such as Webhooks or Git Integrations

### Which customers would this be available to

None

### Acceptance Criteria

- [ ] Allow for multiple "Actions" to be defined in a given Stage of a Pipeline
- [ ] When a user clicks the "play" action of Stage , then the multiple actions in "Stage 2" are all triggered

### Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate

Start by tracing how Pipeline stages and their Actions are represented and how the Stage play action triggers them. Identify the relevant stage editor and execution entry points, then check how existing single-action behavior is tested. Done means a stage can define multiple Actions and playing the stage triggers all of its Actions.

Written by the indexing model from the issue text.