feat: add fine-grained control for link signing (#3924)

* Determine whether the URL requires Sign

* Add File and Mem based KV

NOT TESTED: TokenKV Function

* Change Token KV func to common func.

Add File based KV func

* Remove KV, Remove Token

I found that the original Sign function is enough to complete the link signature, and only need to add simple configuration items to meet the requirements.

* Add IsStorageSigned func to judge if Signing is enabled in the storage settings.

It should be working now.

* Add a SIGN button to the management panel.

* Add enable_sign to the basic storage struct.

Can enable sign for every driver now.

Bug: When sign enabled, in download page, Copy link doesn't contain a sign.

(Not done yet)

* Fix a bug from commit 8f6c25f.

Response of fsread function does not contain sign.

* Optimize code and follow advices.

- Add back public/dist/README.md

- Enable sign when DownProxyUrl is enabled

- Merge needSign() to isEncrypt() in fsread.go

* simplify code

---------

Co-authored-by: Andy Hsu <i@nn.ci>

server/common/check.go

@@ -8,9 +8,15 @@ import (
 	"github.com/alist-org/alist/v3/internal/conf"
 	"github.com/alist-org/alist/v3/internal/driver"
 	"github.com/alist-org/alist/v3/internal/model"
+	"github.com/alist-org/alist/v3/internal/op"
 	"github.com/alist-org/alist/v3/pkg/utils"
 )
 
+func IsStorageSignEnabled(rawPath string) bool {
+	storage := op.GetBalancedStorage(rawPath)
+	return storage != nil && storage.GetStorage().EnableSign
+}
+
 func CanWrite(meta *model.Meta, path string) bool {
 	if meta == nil || !meta.Write {
 		return false