Add Nomic embedding integration

[sky-2002]

This PR adds integration of embeddings with Nomic.

Example usage:

from gptcache.embedding import Nomic

test_sentence = 'Hey this is Nomic embedding integration to gptcache.'
encoder = Nomic(model='nomic-embed-text-v1.5', 
                            api_key='<your-nomic-api-key>', 
                            dimensionality=64)
embed = encoder.to_embeddings(test_sentence)

Note: I have tested this functionality and it works as intended.
Looking forward for review/feedback.

[sre-ci-robot]

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