sidecar to inject qemu args

[ibrokethecloud]

What this PR does

Before this PR:
PR introduces an additional sample sidecar to inject additional qemu args to the domain definition, based on annotations present on the VMI.

After this PR:
Users can fine tune qemu args in the domain definition to control specific behavior.

Fixes #
#11093

Why we need it and why it was done in this way

The following tradeoffs were made:
The sidecar approach seems the least disruptive means to perform this operation without changing core kubevirt api to allow inject of random qemu arguments.

The following alternatives were considered:

Links to places where the discussion took place:
Please refer to conversation from here: #11093 (comment)

Special notes for your reviewer

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[victortoso]

I wrote one in the past too, see #9166 (comment)

[victortoso]

You might be able to write this in python and attach to a configmap and enable it with annotation, instead of having to build a container image.

[victortoso]

If the PR is to be accepted, I'd use libvirtxml instead. This makes the sidecar easy to build out-of-tree. See this one which is not merged yet: #11846

[alicefr]

@ibrokethecloud this should be doable with the configmap that @victortoso mentioned. I would avoid to add an new image. On the other hand, I think we are missing the documentation how to achieve it, @victortoso am I correct? If so, would you mind to add the example in the user guide?

[victortoso]

Hi @alicefr and @ibrokethecloud

I created a simple python script to add qemu env/args using sidecars + configmap and published it as a gist:
https://gist.github.com/victortoso/4a54ef0e75a2b917bb21cb33ec4da141

would you mind to add the example in the user guide?

I'll propose adding it in the user-guide later Today.

Just for clarification, the steps using this example are:

1. The annotation for env/args is: libvirt.vm.kubevirt.io/qemuArgs, see how the data was set here
2. Create the configmap e.g: k create -f examples/my-config-map.yaml
3. Create the VMI (should have sidecar metadata properly set, see it here)

Cheers,