MM-9556 Added ability to upload files without a multipart request (#8306)

* MM-9556 Added ability to upload files without a multipart request

* MM-9556 Handled some unusual test behaviour

api4/context.go

@@ -447,6 +447,18 @@ func (c *Context) RequireFileId() *Context {
 	return c
 }
 
+func (c *Context) RequireFilename() *Context {
+	if c.Err != nil {
+		return c
+	}
+
+	if len(c.Params.Filename) == 0 {
+		c.SetInvalidUrlParam("filename")
+	}
+
+	return c
+}
+
 func (c *Context) RequirePluginId() *Context {
 	if c.Err != nil {
 		return c