feat(platforms): Add helm chart for Vector installation

[alexgavrisco]

This PR adds a helm chart for Vector installation in a K8S cluster.
It's inspired from other similar community helm charts and some ideas are taken from #1900

IMO a community helm chart must support 2 major use cases:

• It should have quite reasonable defaults and allow flexible configuration via --set arguments (or a values file);
• It should allow providing entirely custom configuration (e.g. a configmap created separately of this helm chart) - thus allowing such patterns as "umbrella" deployment with highly specific configuration;

This is why in this helm chart the only source enabled by default (and exposed as separate entity in the sources object) is the kubernetes source. All other components can be easily configuring without coupling helm chart to some specific transforms/sinks.

[alexgavrisco]

Hey @Hoverbear @binarylogic
As a result of discussion on #1900, I've checked that PR, some Vector use-cases (including our current setup) and created this helm chart.
It's flexible enough so I've been able to use it as drop-in replacement for our current Vector installation. And I've tested it with both helm2 and helm3, however only in AWS EKS flavor of Kubernetes.
Please let me know it this approach to the helm chart makes sense to you.

[binarylogic]

Thanks @Alexx-G! It's likely we'll want to finalize #2222 before merging this. This way we'll have consensus on our approach and can review it with that context. Also, feel free to weigh in on that RFC as we update it.

[alexgavrisco]

This totally makes sense. I'll take a look at the RFC, thanks!

[MOZGIII]

Hey! I just wanted to let you know I didn't forget about this PR. This looks great, and soon I'll finally get to reviewing it. We'll likely adopt it after some minor changes to conform to the RFC and our updated YAML configs.

[MOZGIII]

Minor nit: PodSecurityPolicy isn't really a part of RBAC, it should probably be in a separate file and manageable independently.

[binarylogic]

@Alexx-G thank you for taking the time to submit this. I'm going to close this in favor of #2871. Please let us know if we're missing anything that isn't covered here. We're planning to release our official k8s support soon.