[UX] Docs default redirection is not to the latest version

[RukshanJS]

Description:
The direct link for Identity Server docs redirects to docs for an older IS version (5.9.0). (https://is.docs.wso2.com/en/5.9.0/)

Expected - redirect to https://is.docs.wso2.com/en/latest/

Affected Product Version:
5.9.0 and latest

Steps to reproduce:

1. Enter http://docs.wso2.com/identity-server into browser URL bar.
2. The page is redirected to https://is.docs.wso2.com/en/5.9.0/ (not expected)