Add automated test for "Like and Unlike a page"

The manual test is here: Like and Unlike a page

Existing automated coverage

• LikeIT#likeUnlikeDefaultConfiguration: On the main wiki: Like on a WebHome page increments the counter, Unlike decrements it and the value persists after a reload; a terminal page (SubPage) is liked and its counter checked.

Missing automated coverage

• On the main wiki, unlike the terminal page and assert that its counter decreases.
• On a subwiki, like a WebHome page and a terminal page and assert that each counter increases.
• On the subwiki, click the button again on both pages and assert that each counter decreases.

Suggested location: xwiki-platform-core/xwiki-platform-like/xwiki-platform-like-test/xwiki-platform-like-test-docker/src/test/it/org/xwiki/like/test/ui/LikeIT.java

Found by comparing the XWiki 18.4.4 manual test runs against the automated tests on master (a0055f10a1a).