Create redirect for Manage index templates page and remove staging link

### Type of issue

Other

### What documentation page is affected

https://www.elastic.co/docs/manage-data/data-store/templates/index-template-management

### What happened?

The content on this page includes the following:

This page has moved. Refer to [Manage index templates](https://staging-website.elastic.co/docs/manage-data/data-store/index-basics#index-management-manage-index-templates) for all of the steps to create and manage index templates in Kibana.

Fixes to make include:

- Remove page + staging link
- Create a redirect from https://www.elastic.co/docs/manage-data/data-store/templates/index-template-management -> https://www.elastic.co/docs/manage-data/data-store/index-basics#index-management-manage-index-templates

### Additional info

_No response_