Update docker_installation.md

[mkania-cisco]

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[asimpleidea]

Thanks for your contribution @mkania0 and for discovering this!

We will have to change that section of the doc to not have any reference to a hard-coded version as it will be too much of hassle to change it every time we release a new version. See #43.

For now I am going to just close this as it will not be sustainable to keep having hard-coded references.

Thanks again!

[ljakab]

Also, I think we should switch to ghcr.io in our documentation too, since that is our new canonical container registry, even if we still continue pushing to Docker Hub too