feat: add compute roles to assignable organization roles

Owner and Editor gain compute.datumapis.com-admin; Viewer gains
compute.datumapis.com-viewer, so organization members have access
to compute resources consistent with their role level.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: scotwells

config/assignable-organization-roles/roles/datum-cloud-editor.yaml

@@ -24,3 +24,5 @@ spec:
       namespace: milo-system
     - name: dns.networking.miloapis.com-dns-admin
       namespace: milo-system
+    - name: compute.datumapis.com-admin
+      namespace: milo-system

config/assignable-organization-roles/roles/datum-cloud-owner.yaml

@@ -26,3 +26,5 @@ spec:
       namespace: milo-system
     - name: iam-user-invitations-admin
       namespace: milo-system
+    - name: compute.datumapis.com-admin
+      namespace: milo-system

config/assignable-organization-roles/roles/datum-cloud-viewer.yaml

@@ -26,3 +26,5 @@ spec:
       namespace: milo-system
     - name: activity.miloapis.com-viewer
       namespace: milo-system
+    - name: compute.datumapis.com-viewer
+      namespace: milo-system