appview/router: fix url rewriter #798

the appview rewrites urls of the form:

host.com/did-plc-foo/repo => host.com/did:plc:foo/repo
host.com/@handle.com/repo => host.com/handle.com/repo

however, the rewriter did not preserve query parameters or fragments:

host.com/@handle.com/repo?foo=bar => host.com/handle.com/repo?

this resulted in url rewrites being broken for git clones, which usees
the "service" query parameter:

../repo/info/refs?service=git-upload-pack => ../repo/info/refs?

the new url rewriter simply takes the existing url and replaces the path
component, thus preserving all other bits of the url.

Signed-off-by: oppiliappan <me@oppi.li>