support create agit flow pull request (#867)

while looks the alibaba has not maintain
[`git-repo-go`](https://github.com/alibaba/git-repo-go/)
tool, to make agit flow pull requst can be create quickly.
add creating agit flow pull request feature
in tea tool

example:

```SHELL
tea pulls create --agit --remote=origin --topic=test-topic
--title="hello world" --description="test1
test 2
test 3"
```

Signed-off-by: a1012112796 <1012112796@qq.com>
Reviewed-on: https://gitea.com/gitea/tea/pulls/867
Co-authored-by: a1012112796 <1012112796@qq.com>
Co-committed-by: a1012112796 <1012112796@qq.com>

modules/git/repo.go

@@ -4,6 +4,8 @@
 package git
 
 import (
+	"net/url"
+
 	"github.com/go-git/go-git/v5"
 )
 
@@ -33,3 +35,13 @@ func RepoFromPath(path string) (*TeaRepo, error) {
 
 	return &TeaRepo{repo}, nil
 }
+
+// RemoteURL returns the URL of the given remote
+func (r TeaRepo) RemoteURL(remoteName string) (*url.URL, error) {
+	remote, err := r.Remote(remoteName)
+	if err != nil {
+		return nil, err
+	}
+
+	return url.Parse(remote.Config().URLs[0])
+}