collab: Rework model name checks (#16365)

This PR reworks how we do checks for model names in the LLM service.

We now normalize the model names using the models defined in the
database.

Release Notes:

- N/A

crates/collab/src/llm/authorization.rs

@@ -26,9 +26,7 @@ fn authorize_access_to_model(
     }
 
     match (provider, model) {
-        (LanguageModelProvider::Anthropic, model) if model.starts_with("claude-3-5-sonnet") => {
-            Ok(())
-        }
+        (LanguageModelProvider::Anthropic, "claude-3-5-sonnet") => Ok(()),
         _ => Err(Error::http(
             StatusCode::FORBIDDEN,
             format!("access to model {model:?} is not included in your plan"),

crates/collab/src/llm/db.rs

@@ -67,6 +67,21 @@ impl LlmDatabase {
         Ok(())
     }
 
+    /// Returns the names of the known models for the given [`LanguageModelProvider`].
+    pub fn model_names_for_provider(&self, provider: LanguageModelProvider) -> Vec<String> {
+        self.models
+            .keys()
+            .filter_map(|(model_provider, model_name)| {
+                if model_provider == &provider {
+                    Some(model_name)
+                } else {
+                    None
+                }
+            })
+            .cloned()
+            .collect::<Vec<_>>()
+    }
+
     pub fn model(&self, provider: LanguageModelProvider, name: &str) -> Result<&model::Model> {
         Ok(self
             .models