docs: Add ADR for leader elector as extension (#1596)

docs/contributor/arch/013-leader-receiver-creator-as-extension.md

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+# 13. Leader Receiver Creator as Extension
+
+Date: 2024-11-08
+
+## Status
+Proposed
+
+## Context
+
+The Telemetry OTel Collector collects metrics exposed by the Kubernetes API server using [k8sclusterreceiver](https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/receiver/k8sclusterreceiver), 
+and custom resource metrics are collected using [kymastatsreceiver](https://github.com/kyma-project/opentelemetry-collector-components/tree/main/receiver/kymastatsreceiver). 
+To run these receivers in high availability mode and prevent sending duplicate metrics, we've implemented [Singleton Receiver Creator](https://github.com/kyma-project/opentelemetry-collector-components/tree/main/receiver/singletonreceivercreator) based on [Leader Receiver Creator](./012-leader-receiver-creator.md).
+
+## Decision
+However, after feedback from community and careful deliberation, we realize the `singleonreceivercreator` would be better suited to be used as an extension.
+[Extensions](https://github.com/open-telemetry/opentelemetry-collector/blob/main/extension/README.md?plain=1) provide additional functionality to the collector, but do not need direct access to telemetry data and are not part of the pipelines.
+
+Implementing `singleonreceivercreator` as an extension brings the following advantages:
+- It is signal-agnostic.
+- It can be used with any receiver.
+- It brings simpler and clear configuration.
+- It's future-proof.
+
+It has following disadvantages:
+- The receivers must be modified to support the leader election extension.
+
+
+### Leader Election API
+
+```yaml
+receivers:
+  dummy/foo:
+    interval: 1m
+    leaderelector: leaderelector/foo
+  dummy/bar:
+    interval: 1m
+    leaderelector: leaderelector/bar
+extensions:
+  leaderelector/foo:
+    auth_type: kubeConfig
+    lease_name: foo
+    lease_namespace: default
+  leaderelector/bar:
+    auth_type: kubeConfig
+    lease_name: bar
+    lease_namespace: default
+```
+
+The leader elector extension would contain the configuration providing lease name and namespace. This extension would be then referenced in the receivers.
+
+### Consequences
+The Singleton Receiver Creator (https://github.com/kyma-project/opentelemetry-collector-components/tree/main/receiver/singletonreceivercreator) would be deprecated and removed. The `kymastatsreceiver` and `k8sclusterreceiver` would use the leader elector extension for leader election.
+
+The change would also require changes in the `k8sclusterreceiver` to support the leader election extension.
+
+