Add ollama embeddings function (#1263)

Following the docs
[here](https://lancedb.github.io/lancedb/python/python/#lancedb.embeddings.openai.OpenAIEmbeddings)
I've been trying to use ollama embedding via the OpenAI API interface,
but unfortunately I couldn't get it to work (possibly related to
https://github.com/ollama/ollama/issues/2416)

Given the popularity of ollama I thought it could be helpful to have a
dedicated Ollama Embedding function in lancedb.

Very much welcome any thought on this or my code etc. Thanks!

python/python/tests/test_embeddings_slow.py

@@ -45,7 +45,9 @@ except Exception:
 
 
 @pytest.mark.slow
-@pytest.mark.parametrize("alias", ["sentence-transformers", "openai", "huggingface"])
+@pytest.mark.parametrize(
+    "alias", ["sentence-transformers", "openai", "huggingface", "ollama"]
+)
 def test_basic_text_embeddings(alias, tmp_path):
     db = lancedb.connect(tmp_path)
     registry = get_registry()