[MM-20353] Change KVSetWithOptions to accept a byte slice (#13213)

* Drop EncodeJSON from PluginKVSetOptions

* Add unit tests for KVSetWithOptions with nil values

plugin/api.go

@@ -758,13 +758,12 @@ type API interface {
 	KVCompareAndDelete(key string, oldValue []byte) (bool, *model.AppError)
 
 	// KVSetWithOptions stores a key-value pair, unique per plugin, according to the given options.
-	// If options.EncodeJSON is not true, the type of newValue must be of type []byte.
 	// Returns (false, err) if DB error occurred
 	// Returns (false, nil) if the value was not set
 	// Returns (true, nil) if the value was set
 	//
-	// Minimum server version: 5.18
-	KVSetWithOptions(key string, newValue interface{}, options model.PluginKVSetOptions) (bool, *model.AppError)
+	// Minimum server version: 5.20
+	KVSetWithOptions(key string, value []byte, options model.PluginKVSetOptions) (bool, *model.AppError)
 
 	// KVSet stores a key-value pair with an expiry time, unique per plugin.
 	//