add metrics agents (#461)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Introduced new HelmRelease configurations for cert-manager, monitoring
agents, and Victoria Metrics Operator in Kubernetes.
- Added resource specifications for `vmselect` in the VMCluster
configuration.
- Enhanced resource management for `vmselect` with defined limits and
requests for memory and CPU.

- **Bug Fixes**
	- Adjusted resource limits for Redis failover memory allocation.

- **Documentation**
- Updated README and release notes for various components, enhancing
clarity and usability.

- **Chores**
- Updated image versions across multiple components for consistency and
performance improvements.
- Modified migration scripts to facilitate transitions and manage
resources effectively.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: Andrei Kvapil <kvapss@gmail.com>

scripts/migrations/6

@@ -0,0 +1,15 @@
+#!/bin/sh
+# Migration 6 --> 7
+
+# Delete cert-manager crds labels and annotations
+certmanager_crds=$(kubectl get crd -o name | grep '\.cert-manager\.io$')
+if [ -n "$certmanager_crds" ]; then
+  kubectl annotate $certmanager_crds meta.helm.sh/release-namespace=cozy-cert-manager meta.helm.sh/release-name=cert-manager-crds
+  kubectl label $certmanager_crds app.kubernetes.io/managed-by=Helm
+fi
+
+# Remove monitoring, because it is renamed to monitoring-agents
+kubectl get hr -n cozy-monitoring monitoring && kubectl delete hr -n cozy-monitoring monitoring
+
+# Write version to cozystack-version config
+kubectl create configmap -n cozy-system cozystack-version --from-literal=version=7 --dry-run=client -o yaml | kubectl apply -f-