Fix sentence-similarity model URL

[hanouticelina]

Fixes #2494.

This small PR fixes an issue when calling InferenceClient.sentence_similarity() with a model URL.

Issue

Calling InferenceClient.sentence_similarity() using a deployed Inference Endpoint or a localhost URL results in HfHubHTTPError: 422 Client Error.
In general, this is a result of a discrepancy between Inference API and a (local or deployed) inference endpoint.

Fix

adding a /similarity suffix to the model URL. See also TEI OpenAPI doc.

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[Wauplin]

Unfortunately, this issue is not as straightforward to fix as that. Given an Inference Endpoint url, we can't be sure that the model is powered by Text-Embedding-Inference and therefore that we should use the /similarity route. For example, if you go to https://huggingface.co/sentence-transformers/all-mpnet-base-v2 > "Inference Endpoints (dedicated)", the default framework won't be TEI but transformers.

[Wauplin]

Maybe we could check the Inference Endpoint info to get this information (e.g. send a call to model + "/info") but it feels clunky. Ping @osanseviero if you have a better idea on this.

[osanseviero]

cc @tomaarsen for vis