Add ADR on rancher namespace strategy

Signed-off-by: Danil Grigorev <danil.grigorev@suse.com>

docs/adr/0007-rancher-namespace-strategy.md

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+<!-- START doctoc generated TOC please keep comment here to allow auto update -->
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+- [7. Cluster Import Strategy](#7-cluster-import-strategy)
+  - [Context](#context)
+  - [Decision](#decision)
+  - [Consequences](#consequences)
+  - [Sequence Diagram](#sequence-diagram)
+
+<!-- END doctoc generated TOC please keep comment here to allow auto update -->
+
+# 7. Rancher Namespace Strategy
+
+- Status: proposed
+- Date: 2023-16-11
+- Authors: @Danil-Grigorev
+- Deciders: @richardcase @alexander-demicev @furkatgofurov7 @mjura @salasberryfin
+
+## Context
+
+The feature of Rancher Manager allows you to **import** an existing cluster, however, the resources created for the rancher-turtles to use are spawned across randomly generated namespaces, preventing rancher-turtles from using the namespace scoped permissions for the namespace scoped resources within the Rancher Manager cluster.
+
+## Decision
+
+The operator will take the responsibility of placing Rancher resources in a specific namespace, defined by the CAPI cluster resource namespace.
+
+The namespace will only dictate the designated location of the Rancher Manager cluster resources, such as **provisioning.cattle/v1.Cluster** and **management.cattle/v3.ClusterRegistrationToken**.
+
+## Consequences
+
+To replicate the import steps the operator will need to change the [import strategy][] in steps 1 to 2:
+
+1. Create an instance of the **provisioning.cattle/v1.Cluster** in the Rancher Manager cluster in the selected namespace. Wait for the cluster name to be provided in the status subresource.
+1. Create an instance of the **management.cattle/v3.ClusterRegistrationToken** for the cluster name in the selected namespace. Wait for the **ClusterRegistrationToken** status to be populated AND contain an import URL.
+
+The rest of the steps of the [import strategy][] are unchanged.
+
+[import strategy]: ./0006-import-strategy.md#consequences
+
+### Sequence Diagram
+
+![diagram](./images/import-sequence.png)