Adding "longrope" for Phi-3 (#2172)

[amihalik]

What does this PR do?

Updates the rope scaling type check for Phi-3 to include "longrope".

I implemented and tested these changes using this process:

1. Launched latest TGI docker container on an aws g6.2xlarge
2. Modified /opt/conda/lib/python3.10/site-packages/text_generation_server/layers/rotary.py in the container
3. Ran text-generation-launcher --model-id microsoft/Phi-3-mini-128k-instruct --trust-remote-code
4. Validated that Phi-3 loaded
5. Executed queries against the endpoint and validated responses from TGI

Fixes #2172

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[danieldk]

Awesome, from a diff against their two model revisions it indeed seems that they just renamed the embeddings from su to longrope.

Thanks!