Add CTA section to work pages of 'publication' type

[r-ferrier]

Description

A CTA section is added above the main content for a publication work page. This section contains buttons, whose names and onclick actions are defined in the markdown. This section should only appear when buttons exist on the markdown and should be able to contain any number of buttons. Initially, the buttons just need to be able to link to external sites.

design file here

Acceptance criteria

• [ ] I can add a button title and destination to a work markdown file and see it displayed in a CTA section on the website
• [ ] Every button I have added is displayed in the order they are written in the markdown file
• [ ] At desktop and mobile buttons are displayed in a row which wraps when there are too many to fit on one line
• [ ] Clicking on a button can take me to an internal or external page