[docs] Add RFC for managed CR

docs/rfcs/managed.md

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+# TITLE
+
+**Status:** *Draft*
+
+**Author:** Antoine Toulme (@atoulme)
+
+**Date:** 2025-03-20
+
+## Objective
+
+Condense all best practices and deployment patterns of OpenTelemetry components into a single custom resource
+that covers the feature set of the OpenTelemetry Helm chart.
+
+## Summary
+This request for comment aims to establish a new approach to management of resources in Kubernetes clusters,
+specifically in Openshift environments, with the explicit goal of taking over the whole cluster, and making decisions
+on how to best instrument all resources in the cluster on behalf of the administrator based on best practices,
+OpenTelemetry standards and semantic conventions.
+
+The operator project offers custom resources (CR) to allow Kubernetes operators to define OpenTelemetry components
+in their Kubernetes environments. Customers however do not want to manage components themselves, especially if they need
+to think about component versioning and upgrade patterns, and would rather have an out-of-the-box experience that 
+requires little insight and gets them to a working state effortlessly.
+
+## Goals and non-goals
+
+### Give a comprehensive, out-of the box experience of OpenTelemetry for a first-time user
+The goal is to delight first-time customers by giving them a complete view of what is possible with OpenTelemetry.
+
+### Do not offer a way to turn on and off specific features
+We mean to offer a specific functional coverage of a specific use case that offers best practices of OpenTelemetry.
+
+We don't allow to toggle features in and out specifically because we want to avoid increasing the need for functional test coverage.
+
+If customers want to increase their level of control of the feature set, they can remove the managed custom resource and instead
+follow the traditional route of setting up collectors, target allocators, instrumentation custom resources as is possible today.
+
+## Use cases for proposal
+
+### Initial installation
+
+The customer wants to install the operator and immediately get value from the installation.
+
+Upon installation, they install the custom resource with information on an OTLP endpoint where they can direct all data.
+
+### Upgrade
+
+The customer wants to upgrade their operator. All assets are upgraded out of the box in concert as part of the upgrade,
+and are guaranteed to work through functional test coverage.
+
+### Deletion and reinstallation
+
+The customer can cleanly delete the custom resource, which triggers the deletion of all OpenTelemetry assets under
+management by the operator. No stragglers are left.
+
+### Kubernetes metrics
+
+The customer upon installation of the custom resource can see Kubernetes cluster metrics as reported by the k8sclusterreceiver with default configuration.
+
+### Kubeletstats metrics
+
+The customer upon installation receives metrics from all Kubeletstats metrics from the default configuration of the kubeletstats receiver.
+
+### Automatic instrumentation
+
+All standard CRDs for instrumentations are all enabled by default for all namespaces.
+
+### Node host metrics
+
+The customer upon installation receives metrics from hostmetrics receiver with its default configuration.
+
+Note the metrics map to the host, meaning the collector will have access to host volumes to scrape their utilization.
+
+### Node logs
+
+The customer upon installation will receive all logs from Kubernetes, scraped with the filelog receiver from the file system.
+
+### Kubernetes entities
+
+When entities become viable, the customer will receive Kubernetes entities as reported by the k8sclusterreceiver.
+
+## Struct Design
+
+```go
+import "go.opentelemetry.io/collector/exporter/otlpexporter"
+
+type ManagedCustomResource struct {
+	ExporterConfig otlpexporter.Config `yaml:"exporter"`
+}
+```
+
+```yaml
+---
+apiVersion: apiextensions.k8s.io/v1
+kind: CustomResourceDefinition
+metadata:
+  annotations:
+    controller-gen.kubebuilder.io/version: v0.32.0
+  name: managed.opentelemetry.io
+spec:
+  group: opentelemetry.io
+  names:
+    kind: Managed
+    listKind: ManagedList
+    plural: manageds
+    singular: managed
+  scope: Cluster
+  versions:
+  - additionalPrinterColumns:
+    - jsonPath: .metadata.creationTimestamp
+      name: Age
+      type: date
+    - jsonPath: .spec.exporter.endpoint
+      name: Endpoint
+      type: string
+    name: v1alpha1
+    schema:
+      openAPIV3Schema:
+        properties:
+          apiVersion:
+            type: string
+          kind:
+            type: string
+          metadata:
+            type: object
+          spec:
+            properties:
+              exporter:
+                <OTLP exporter config>
+            type: object
+        type: object
+    served: true
+    storage: true
+
+```
+## Rollout Plan
+
+See https://github.com/open-telemetry/opentelemetry-operator/issues/3818
+
+## Limitations
+
+This managed resource is not aiming to please all users of the operator. This is a limited experience to deliver best practices and a comprehensive feature set encompassing many elements of OpenTelemetry.