Allow users to use a single design template with snippets for each step of a journey

[mdnew]

Is your feature request related to a problem?

Yes

Please describe.

If I need to make changes to the design of my template. I don't want to have to update each template for each step. It would be easier if there was a single design template for a journey that I could update once.

Describe the solution you'd like

For each journey, I specify the design template to use. Then for each step, I can put in the custom HTML / text that needs to be inserted for that step.

Describe alternatives you've considered

Right now, I've created a similar system locally using MJML but it would better if LaudSpeaker was the source of truth.

Additional context

Thank you for your feature request – we love each and every one!