Update legacy-url-mappings.yml for ECK versions dropdown (#1654)

Showing 3.0+ for ECK new docs.

Author: eedugon

config/legacy-url-mappings.yml

@@ -32,7 +32,7 @@ mappings:
   en/beats/topbeat/: *stack
   en/beats/winlogbeat/: *stack
   en/cloud-heroku/: []
-  en/cloud-on-k8s/: [ '3.0.0', '2.16', '2.15', '2.14', '2.13', '2.12', '2.11', '2.10', '2.9', '2.8', '2.7', '2.6', '2.5', '2.4', '2.3', '2.2', '2.1', '2.0', '1.9', '1.8', '1.7', '1.6', '1.5', '1.4', '1.3', '1.2', '1.1', '1.0' ]
+  en/cloud-on-k8s/: [ '3.0+', '2.16', '2.15', '2.14', '2.13', '2.12', '2.11', '2.10', '2.9', '2.8', '2.7', '2.6', '2.5', '2.4', '2.3', '2.2', '2.1', '2.0', '1.9', '1.8', '1.7', '1.6', '1.5', '1.4', '1.3', '1.2', '1.1', '1.0' ]
   en/cloud/: []
   en/cloud-enterprise/: [ '4.0', '3.8', '3.7', '3.6', '3.5', '3.4', '3.3', '3.2', '3.1', '3.0', '2.13', '2.12', '2.11', '2.10', '2.9', '2.8', '2.7', '2.6', '2.5', '2.4', '2.3', '2.2', '2.1', '2.0', '1.1', '1.0' ]
   en/ecctl/: [ '1.14+', '1.13', '1.12', '1.11', '1.10', '1.9', '1.8', '1.7', '1.6', '1.5', '1.4', '1.3', '1.2', '1.1', '1.0' ]