support base_url path for model providers (#608)

* adding support for base_url

* updated docs

* fixed tests for config generator

* making fixes based on PR comments

---------

Co-authored-by: Salman Paracha <salmanparacha@MacBook-Pro-288.local>

crates/common/src/configuration.rs

@@ -267,6 +267,7 @@ pub struct LlmProvider {
     pub usage: Option<String>,
     pub routing_preferences: Option<Vec<RoutingPreference>>,
     pub cluster_name: Option<String>,
+    pub base_url_path_prefix: Option<String>,
 }
 
 pub trait IntoModels {
@@ -307,6 +308,7 @@ impl Default for LlmProvider {
             usage: None,
             routing_preferences: None,
             cluster_name: None,
+            base_url_path_prefix: None,
         }
     }
 }