Cypress tests for the Synonyms feature

[felipeelia]

Description of the Change

This PR adds cypress tests related to the Synonyms feature.

• Create a synonym set with “hoodie” and “sweatshirt” -> ensure searching for “sweatshirt” returns the hoodie from the WC sample data
• Delete all synonym sets and synonym alternatives, test “sweatshirt” again to ensure “hoodie” no longer matches
• Add an alternative with a primary term of “sweater” and a term of “hoodie”, then search for “sweater” and expect the result of “hoodie” to appear. Repeat search with “hoodie” and expect only hoodie (but not sweater) to appear.
• Delete all synonym sets one more time to confirm the dashboard is still working.
• Switching to the “Advanced Text Editor” allows the user to:
  • Create new lines
  • Freely edit existent sets of synonyms
  • Give proper warning for wrong entries (a line with only “word =>” for example)
• Index via WP-CLI and verify if the synonyms previously set weren’t removed

Related to #2614

Changelog Entry

Added: e2e tests for the Synonyms feature.

Credits

Props @felipeelia