acc-backend not found: does not exist or no pull access

Hi,

Thanks for creating the agent-control-center app for managing the agents; I was giving a try and blocked on non-existing docker repo -

```
Starting docker-compose with images from [appdynamics]

[+] Running 0/2
⠧ acc-frontend Pulling 0.8s
⠧ acc-backend Pulling
``` 0.8s
**`repository docker.io/appdynamics/acc-backend not found: does not exist or no pull access`**

Start with the docker-compose setup that requests appdynamics/acc-backend and verify whether that image exists and is accessible. Reproduce the pull failure; done means the compose startup can obtain the backend image without the reported not-found or access error.

Written by the indexing model from the issue text.