Draft: Explain the role of agentk in the flux setup tutorial

What does this MR do?

This MR suggests to enhance the documentation for the flux setup tutorial - https://docs.gitlab.com/ee/user/clusters/agent/gitops/flux_tutorial.html.

I personally found it confusing to understand why flux needs support of agentk. It appeared overly complex and is lacking explanation imho. Agentk and gitops pull is deprecated and it is clear to some that operational container scanning and the integration with the CI pipeline are still a task for agentk. Now when the flux setup tutorial is mentioning to also install agentk, the question I was asked is why. If someone considers to use rather ArgoCD you would not think of combining it with agentk either. Which leads down to explaining the reason.

I learned the following from @nagyv-gitlab

The tutorial installs agentk for two reasons:

• to make a more feature-full experience including the cluster UI
• to show how one can install a Helm chart with Flux

My suggestion would be to make it explicit that agentk is not used for gitops pull in any way and is being installed for those two reasons above and what else might be relevant. It'd be further helpful to link to the full description of tasks of agentk from there as well and also to the deprecated use case.

So, it is becoming perfectly clear that you can have flux without agentk but have certain disadvantages and missing UI capabilities?

Cheers, Mirko

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