Add from_config to sampler

Every class with a get_config should have a from_config somewhere in
the super() chain. This is actually causing test failures on nightly.

Author: mattdangerw

keras_nlp/samplers/sampler.py

@@ -377,6 +377,10 @@ def one_step(
         )
         return prompt
 
+    @classmethod
+    def from_config(cls, config):
+        return cls(**config)
+
     def get_config(self):
         return {
             "jit_compile": self.jit_compile,