[FEATURE] Merge the Docker image pipeleins into the main pipeline

**Is your feature request related to a problem? Please describe.**

When a PR is approved there are two pipelines that run. One that builds the docker image for DockerHub and the other that actually deploys the API to app service.

It's setup like this as it was easier to containerise it this way and get the dev environment working. However the docker image should represent what is live. Changes only go live after the manual approval gate so the docker image should only be produced after this gate.

**Describe the solution you'd like**

Merge the task from the create docker pipeline into the main pipeline and after the manual approval gate to run in parallel to the deploy to live action.

**Describe alternatives you've considered**

We're operating the alterative which doesn't really support a quality docker image and could cause confusion if the image is produced and found to be faulty.

**Additional context**