Add replicate take 2 (#2077)

This PR adds a replicate integration to langchain. 

It's an updated version of
https://github.com/hwchase17/langchain/pull/1993, but with updates to
match latest replicate-python code.
https://github.com/replicate/replicate-python.

---------

Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>
Co-authored-by: Zeke Sikelianos <zeke@sikelianos.com>

tests/integration_tests/llms/test_replicate.py

@@ -0,0 +1,10 @@
+"""Test Replicate API wrapper."""
+
+from langchain.llms.replicate import Replicate
+
+
+def test_replicate_call() -> None:
+    """Test valid call to Replicate."""
+    llm = Replicate()
+    output = llm("Say foo:")
+    assert isinstance(output, str)