add aleph alpha llm (#1207)

Integrate Aleph Alpha's client into Langchain to provide access to the
luminous models - more info on latest benchmarks here:
https://www.aleph-alpha.com/luminous-performance-benchmarks

tests/integration_tests/llms/test_aleph_alpha.py

@@ -0,0 +1,10 @@
+"""Test Aleph Alpha API wrapper."""
+
+from langchain.llms.aleph_alpha import AlephAlpha
+
+
+def test_aleph_alpha_call() -> None:
+    """Test valid call to cohere."""
+    llm = AlephAlpha(maximum_tokens=10)
+    output = llm("Say foo:")
+    assert isinstance(output, str)