Configurable option to display footer's content as a right sidebar

Implement a configurable option to display the footer's content as a right sidebar. Check [Vintage Spirits and Forgotten Cocktails](https://forgottencocktails.com) as an example. By default, when `displayFooterAsRightSidebar = false`, it should be displayed as before. But when `displayFooterAsRightSidebar = true`, the footer's content should be displayed on the right. See this [discussion](https://github.com/Lednerb/bilberry-hugo-theme/discussions/677) for more details.