fix(deployment reconciler): Couldn't parse image reference "docker.io/grafana/grafana@9.1.6"

[sonnyg]

To Reproduce

1. Perform a basic helm deployment (flux in my case) of the grafana-operater.
2. Create a sample Grafana and GrafanaDashboard resource.

Result

The resultant Deployment artifact produces the following error:

Warning  InspectFailed  9s (x11 over 2m7s)  kubelet            Failed to apply default image tag "docker.io/grafana/grafana@9.1.6": couldn't parse image reference "docker.io/grafana/grafana@9.1.6": invalid reference format
Warning  Failed         9s (x11 over 2m7s)  kubelet            Error: InvalidImageName

After some checking, I found the cause related to a recent change made to the deployment_reconciler.go file. The issue seemed straightforward enough, so I made the fix and added some tests.

I have never done go before, so please accept my apologies if I made any mistakes.

Thank you for your consideration and review.

[NissesSenap]

Thanks allot @sonnyg , we apparently didn't do a very good job in verifying the last major change.
I will merge your PR directly and cut a new release.

[sonnyg]

You are very welcome @NissesSenap . I am very thankful for this project and I'm glad I was able to help out!