Fix implicit image naming and tagging for vc-nimbus

[TobiWo]

Summary

The image created during the build is generated without an explicit tag. This causes a docker compose up -d , after a version bump, to not update the nimbus container out of the box. Instead you need to stop and remove manually and then remove the actual image from the local registry.

Solution

Add an explicit image name and use the current nimbus version tag for the created image.

Downside

The default version needs to be set on two lines. The better approach would be to fully rely on the .env file and only maintain version there. However, this deviates from all other provided compose.

[OisinKyne]

The default version needs to be set on two lines.

Where else does it need to be set? :) this pr has only one. When we add nimbus as a cl maybe?

[TobiWo]

Hi @OisinKyne , as far as I can see there is no cl-nimbus defined yet. So I think we are good to go 👍 . Thanks for merging.