Only follow robots.txt redirects on the same host

[rzo1]

HttpRobotRulesParser resolved the Location header of a robots.txt redirect and re-fetched it without checking scheme, host or port, so the fetch could end up on any host the redirect named. It is now followed only when the target is http or https and shares scheme, host and port with the URL it was reached from; otherwise the response is treated like any other that yields no rules.

Sites serving robots.txt through a redirect to another host, a CDN for instance, are affected: http.robots.redirect.crosshost.allow (default false) restores the old behaviour for http and https targets. Documented in crawler-default.yaml and configuration.adoc.

For all changes

• Is there a issue associated with this PR? Is it referenced in the commit message? - no issue

• Does your PR title start with #XXXX where XXXX is the issue number you are trying to resolve? - no issue

• Has your PR been rebased against the latest commit within the target branch (typically main)?

• Is your initial contribution a single, squashed commit?

• Is the code properly formatted with mvn git-code-format:format-code -Dgcf.globPattern="**/*" -Dskip.format.code=false?

For code changes

• Have you ensured that the full suite of tests is executed via mvn clean verify? - core module tests only
• Have you written or updated unit tests to verify your changes? - new HttpRobotRulesParserRedirectTargetTest; the existing redirect test sets the new key, since its chain crosses ports
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0? - no new dependencies
• If applicable, have you updated the LICENSE file, including the main LICENSE file? - n/a
• If applicable, have you updated the NOTICE file, including the main NOTICE file? - n/a