Add the ability to customize available models for OpenAI-compatible services (#13276)

Closes #11984, closes #11075.

Release Notes:

- Added the ability to customize available models for OpenAI-compatible
services ([#11984](https://github.com/zed-industries/zed/issues/11984))
([#11075](https://github.com/zed-industries/zed/issues/11075)).


![image](https://github.com/zed-industries/zed/assets/32017007/01057e7b-1f21-49ad-a3ad-abc5282ffaf0)

crates/open_ai/src/open_ai.rs

@@ -55,6 +55,8 @@ pub enum Model {
     #[serde(rename = "gpt-4o", alias = "gpt-4o-2024-05-13")]
     #[default]
     FourOmni,
+    #[serde(rename = "custom")]
+    Custom { name: String, max_tokens: usize },
 }
 
 impl Model {
@@ -74,15 +76,17 @@ impl Model {
             Self::Four => "gpt-4",
             Self::FourTurbo => "gpt-4-turbo-preview",
             Self::FourOmni => "gpt-4o",
+            Self::Custom { .. } => "custom",
         }
     }
 
-    pub fn display_name(&self) -> &'static str {
+    pub fn display_name(&self) -> &str {
         match self {
             Self::ThreePointFiveTurbo => "gpt-3.5-turbo",
             Self::Four => "gpt-4",
             Self::FourTurbo => "gpt-4-turbo",
             Self::FourOmni => "gpt-4o",
+            Self::Custom { name, .. } => name,
         }
     }
 
@@ -92,12 +96,24 @@ impl Model {
             Model::Four => 8192,
             Model::FourTurbo => 128000,
             Model::FourOmni => 128000,
+            Model::Custom { max_tokens, .. } => *max_tokens,
         }
     }
 }
 
+fn serialize_model<S>(model: &Model, serializer: S) -> Result<S::Ok, S::Error>
+where
+    S: serde::Serializer,
+{
+    match model {
+        Model::Custom { name, .. } => serializer.serialize_str(name),
+        _ => serializer.serialize_str(model.id()),
+    }
+}
+
 #[derive(Debug, Serialize)]
 pub struct Request {
+    #[serde(serialize_with = "serialize_model")]
     pub model: Model,
     pub messages: Vec<RequestMessage>,
     pub stream: bool,