Allow renaming/moving binary/LFS files in the UI (#34350)

Adds the ability to rename/move binary files like binary blobs or images
and files that are too large in the web ui.
This was purposed in #24722, along with the ability edit images via an
upload of a new image, which I didn't implement here (could be done in a
separate PR).

Binary file content:

![binary](https://github.com/user-attachments/assets/61d9ff71-25d3-4832-9288-452cdefc7283)

File too large:

![toolarge](https://github.com/user-attachments/assets/3b42dbd0-e76a-4c3c-92d2-52ebffedea64)

GitHub does the same (I've copied the text from there):

![gh](https://github.com/user-attachments/assets/e1499813-fb71-4544-9d58-086046a5f13e)

services/forms/repo_form.go

@@ -10,6 +10,7 @@ import (
 
 	issues_model "code.gitea.io/gitea/models/issues"
 	project_model "code.gitea.io/gitea/models/project"
+	"code.gitea.io/gitea/modules/optional"
 	"code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/modules/web/middleware"
 	"code.gitea.io/gitea/services/context"
@@ -689,7 +690,7 @@ func (f *NewWikiForm) Validate(req *http.Request, errs binding.Errors) binding.E
 // EditRepoFileForm form for changing repository file
 type EditRepoFileForm struct {
 	TreePath      string `binding:"Required;MaxSize(500)"`
-	Content       string
+	Content       optional.Option[string]
 	CommitSummary string `binding:"MaxSize(100)"`
 	CommitMessage string
 	CommitChoice  string `binding:"Required;MaxSize(50)"`