Add e2e test for directory's external links

[fdalcin]

Create a test spec for all the external links that exist inside the directory.

Links that have to be tested:

• [x] Learn more about PressbooksEDU button
• [x] Pressbooks logo
• [x] Algolia logo
• [x] Social media icons

In addition, all links should be added to the src/store/modules/config.js file instead of being hardcoded in the HTML.

[fdalcin]

Algolia already provides a powered by component with tests.