Update image tag format in compose.yaml

[danielr1996]

Otherwise docker compose up fails with

 ✘ omni Error failed to resolve reference "ghcr.io/siderolabs/omni:1.3.4": ghcr.io/siderolabs/omni:1.3.4: not found                                                                   1.3s

[Unix4ever]

I don't think it's a good idea to change it like that now. All docs are adding v prefix to the OMNI_IMG_TAG when you set the env var. Changing that to prepend v inside the compose file will render all of them unusable.

I guess our official documentation needs to be fixed as it's using incorrect format there.

[danielr1996]

Thats if course also possible, i just wanted to the sidero team to be aware that the current documentation contains issues, maybe I should have created an issue instead.

[Unix4ever]

Fixed the docs here https://github.com/siderolabs/docs/pull/184

[Unix4ever]

The documentation fix was merged.

[danielr1996]

Thanks for fixing it, but now it must also be updated in the curl https://raw.githubusercontent.com/siderolabs/omni/v${OMNI_VERSION}/deploy/compose.yaml -o compose.yaml command, I created a pull request: https://github.com/siderolabs/docs/pull/187