Add ADR

Signed-off-by: Brad Davidson <brad.davidson@rancher.com>
(cherry picked from commit 612473755d)

docs/adrs/core-controller-user.md

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+# Use a dedicated user for K3s core controllers
+
+Date: 2023-05-26
+
+## Status
+
+Accepted
+
+## Context
+
+Users who collect audit logs from K3s currently have a hard time determining if an action was performed by an administrator, or by the K3s supervisor.
+This is due to the K3s supervisor using the same `system:admin` user for both the admin kubeconfig, and the kubeconfig used by core Wrangler controllers that drive core functionality and the deploy/helm controllers.
+
+Users may have policies in place that prohibit use of the `system:admin` account, or that require service accounts to be distinct from user accounts.
+
+## Decision
+
+* We will add a new kubeconfig for the K3s supervisor controllers: core functionality, deploy (AddOns; aka the manifests directory), and helm (HelmChart/HelmChartConfig).
+* Each of the three controllers will use a dedicated user-agent to further assist in discriminating between events, via both audit logs and resource ManageFields tracking.
+* The new user account will use exisiting core Kubernetes group RBAC.
+
+## Consequences
+
+* K3s servers will create and manage an additional kubeconfig, client cert, and key that is intended only for use by the supervisor controllers.
+* K3s supervisor controllers will use distinct user-agents to further discriminate between which component initiated the request.