ai: Separate model settings for each feature (#28088)

Closes: https://github.com/zed-industries/zed/issues/20582

Allows users to select a specific model for each AI-powered feature:
- Agent panel
- Inline assistant
- Thread summarization
- Commit message generation

If unspecified for a given feature, it will use the `default_model`
setting.

Release Notes:

- Added support for configuring a specific model for each AI-powered
feature

---------

Co-authored-by: Danilo Leal <daniloleal09@gmail.com>
Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>

crates/git_ui/src/git_panel.rs

@@ -37,7 +37,8 @@ use gpui::{
 use itertools::Itertools;
 use language::{Buffer, File};
 use language_model::{
-    LanguageModel, LanguageModelRegistry, LanguageModelRequest, LanguageModelRequestMessage, Role,
+    ConfiguredModel, LanguageModel, LanguageModelRegistry, LanguageModelRequest,
+    LanguageModelRequestMessage, Role,
 };
 use menu::{Confirm, SecondaryConfirm, SelectFirst, SelectLast, SelectNext, SelectPrevious};
 use multi_buffer::ExcerptInfo;
@@ -3764,8 +3765,9 @@ fn current_language_model(cx: &Context<'_, GitPanel>) -> Option<Arc<dyn Language
     assistant_settings::AssistantSettings::get_global(cx)
         .enabled
         .then(|| {
-            let provider = LanguageModelRegistry::read_global(cx).active_provider()?;
-            let model = LanguageModelRegistry::read_global(cx).active_model()?;
+            let ConfiguredModel { provider, model } =
+                LanguageModelRegistry::read_global(cx).commit_message_model()?;
+
             provider.is_authenticated(cx).then(|| model)
         })
         .flatten()