Hide visibility Subscription-agreement-1.4.njk from handbook

### Description

Make the page /handbook/customer/sales/subscription-agreement-1.4.njk into a hidden page on the website.
1.5 replaces 1.4 and is no longer used with new contracts.

### Epic/Story

_No response_

### Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate

Start with /handbook/customer/sales/subscription-agreement-1.4.njk and inspect how handbook pages are made hidden on the website. Make this 1.4 page hidden while leaving the replacement 1.5 page available; done means the 1.4 page is no longer visible in the handbook.

Written by the indexing model from the issue text.