Make git clone URL could use current signed-in user (#33091)

close #33086

* Add a special value for "SSH_USER" setting: `(DOER_USERNAME)`
* Improve parseRepositoryURL and add tests (now it doesn't have hard
dependency on some setting values)

Many changes are just adding "ctx" and "doer" argument to functions.

By the way, improve app.example.ini, remove all `%(key)s` syntax, it
only makes messy and no user really cares about it.

Document: https://gitea.com/gitea/docs/pulls/138

modules/httplib/url.go

@@ -5,6 +5,7 @@ package httplib
 
 import (
 	"context"
+	"net"
 	"net/http"
 	"net/url"
 	"strings"
@@ -81,6 +82,12 @@ func GuessCurrentHostURL(ctx context.Context) string {
 	return reqScheme + "://" + req.Host
 }
 
+func GuessCurrentHostDomain(ctx context.Context) string {
+	_, host, _ := strings.Cut(GuessCurrentHostURL(ctx), "://")
+	domain, _, _ := net.SplitHostPort(host)
+	return util.IfZero(domain, host)
+}
+
 // MakeAbsoluteURL tries to make a link to an absolute URL:
 // * If link is empty, it returns the current app URL.
 // * If link is absolute, it returns the link.
@@ -105,7 +112,7 @@ func IsCurrentGiteaSiteURL(ctx context.Context, s string) bool {
 		if cleanedPath == "" || cleanedPath == "." {
 			u.Path = "/"
 		} else {
-			u.Path += "/" + cleanedPath + "/"
+			u.Path = "/" + cleanedPath + "/"
 		}
 	}
 	if urlIsRelative(s, u) {