Scores returned by Astra are not comparable to Similarity Score

[bjchambers]

Describe the bug
Astra returns a similarity score normalized to [0, 1]. cosine_similarity function returns a score in the range [-1, 1].

These can be converted:

• To Astra: (x + 1.0) / 2.0
• From Astra: (x / 2.0) - 1.0

This matters when we are sorting elements by score, since the two will not be comparable.

Expected behavior

We should probably have the Astra adapter convert to the values returned from cosine_similarity.

[bjchambers]

Also may be worth have the Astra adapter verify the collection is configured to use cosine similarity (instead of other metrics).