Add automated test for "Change Avatar Image Select Another Image"

The manual test is here: Change Avatar Image Select Another Image

Existing automated coverage

• UserProfileIT#changeAvatarImage: Opens Change photo, uploads a first image, submits and asserts the profile avatar is that image.

Related: XWIKI-24757 (open) asks for broader functional tests of the attachment selector macro used by this dialog.

Missing automated coverage

• After a first avatar is set, click Change photo again and upload a second, different image
• Submit and assert the profile avatar is now the second image and no longer the first one

Suggested location: xwiki-platform-core/xwiki-platform-user/xwiki-platform-user-profile/xwiki-platform-user-profile-test/xwiki-platform-user-profile-test-docker/src/test/it/org/xwiki/user/test/ui/UserProfileIT.java

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