feat: Introduce possibility to install VictoriaMetrics or Prometheus

[mglotov]

PR Description

• Introduced possibility to choose between VictoriaMetrics and Prometheus. VictoriaMetrics is a default option. I decided to duplicate all staff related to grafana and alertmanager for VictoriaMetrics and Prometheus because this is the easiest way of having two options at the same time.
• Added notes about it in the FAQ.md
• Upgraded kube-prometheus-stack to the 19.3.0 version. Couldn't upgrade it to the latest because of this issue [kube-prometheus-stack] Can't upgrade CRD from 0.50.0 to 0.52.0: metadata.annotations: Too long: must have at most 262144 bytes prometheus-community/helm-charts#1500
• This PR changed the way of installing Prometheus' CRDs. They are installed separately now. I tried to use terraform kubernetes provider to install kubernetes manifests (CRDs in this case). However, faced an error:

│ Error: Forbidden attribute key in "manifest" value
│
│   with kubernetes_manifest.prometheus-operator_crds["alertmanagerconfigs.monitoring.coreos.com"],
│   on eks-prometheus-operator-crds.tf line 21, in resource "kubernetes_manifest" "prometheus-operator_crds":
│   21: resource "kubernetes_manifest" "prometheus-operator_crds" {
│
│ 'status' attribute key is not allowed in manifest configuration

It describes here hashicorp/terraform-provider-kubernetes#1428.

That's why I switched from kubernetes provider to kubectl provider. It supports additional functionality https://github.com/gavinbunney/terraform-provider-kubectl/blob/15de61bb38d402fff44db5ea6b1cc8d43aea579a/docs/resources/kubectl_manifest.md#ignore-manifest-fields

Fixes #145

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation

[sonarcloud]

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