Allow UrlRewriter to override protocol

[denyska]

Description of the problem / feature request:

Allow UrlRewriter to re-write protocol along with hostname. i.e. https -> http, http -> https. At the moment Urlrewriter assumes the same protocol will be used.

Feature requests: what underlying problem are you trying to solve with this feature?

UrlRewriter's main use case is to point public urls to private artifact repositories. Some of the internal repos are HTTP-only. For ex., we run forwarding proxy as side car on the build agents. The proxy internally forwards and caches requests to central artifact storage that uses complex authentication. There is no security/performance benefits of running this proxy with HTTPS enabled.

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

N/A

What operating system are you running Bazel on?

MacOS

What's the output of bazel info release?

bazel info release

If bazel info release returns "development version" or "(@non-git)", tell us how you built Bazel.

N/A

What's the output of git remote get-url origin ; git rev-parse master ; git rev-parse HEAD ?

N/A

Have you found anything relevant by searching the web?

Nope

Any other information, logs, or outputs that you want to share?

N/A