Add Rancher Security Best Practices to version 2.7 and 2.8

versioned_sidebars/version-2.7-sidebars.json

@@ -1075,6 +1075,7 @@
               ]
             },
             "reference-guides/rancher-security/kubernetes-security-best-practices",
+            "reference-guides/rancher-security/rancher-security-best-practices",
             "reference-guides/rancher-security/security-advisories-and-cves",
             "reference-guides/rancher-security/psa-restricted-exemptions"
           ]