Separate gender balance promo into a partial

[octopusinvitro]

Problem

At the moment, the gender-balance section is hard-coded in two different pages, the Country page and the House page. Since it is the same bit of code, if we make changes to it on one page, we have to remember to make the same changes in the other page.

Proposed Solution

Separate that section into its own partial and inject it in the above mentioned pages.

Acceptance Criteria

Making changes to that section does not require to remember to make changes in all the pages were the section is hardcoded, but just in one place (the partial).