Previously, the HAL browser endpoint did not consider the dispatcher
servlet’s path (server.servlet-path) when redirecting to browser.html
or when updating the API entry point in the served HTML.

This commit moves to using ServletUriComponentsBuilder to build the URI
for the redirect and the path for the entry point. In the interests of
simplicity the logic that sometimes redirected and sometimes forwarded
the request has been changed so that it will always perform a redirect.

Closes gh-6586