SEO Robots Tags not inherited

## Feature Request

**Is your feature request related to a problem? Please describe.**
In the Pageproperties --> Tab Advances --> at the bottom. You can add Robots Tags. This is working.
The Properties should be inherited to subpages if nothing is selcted in the child Page. This would be more userfriendly. Instead of set the Property on each page.

**Describe the solution you'd like**
Changes in page head.html would solve the Problem
From:
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To:
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**Are there alternatives?**
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Start by locating the page head.html referenced in the issue and compare the current page.robotsTags expression with the proposed inheritedPageProperties['cq:robotsTags'] expression. Done means child pages with no selected robots tags render the inherited value while explicitly set child values continue to work.

Written by the indexing model from the issue text.