Adding Granite 7b Instruct model example (#2487)

* Adding Granite 7b Instruct model example

* Minor refactoring to make it a little more idiomatic

* Clippy fixes.

* * Adding a README with some information about supported Granite models
* Changing the default prompt to accomodate better the Language
  modality of the Granite 7b Instruct model

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Co-authored-by: Laurent <laurent.mazare@gmail.com>

candle-transformers/src/models/mod.rs

@@ -24,6 +24,7 @@ pub mod flux;
 pub mod gemma;
 pub mod gemma2;
 pub mod glm4;
+pub mod granite;
 pub mod hiera;
 pub mod jina_bert;
 pub mod llama;