Rename assistant_settings to agent_settings (#31513)

This PR renames the `assistant_settings` crate to `agent_settings`, as
well a number of constructs within it.

Release Notes:

- N/A

crates/git_ui/Cargo.toml

@@ -17,9 +17,9 @@ default = []
 test-support = ["multi_buffer/test-support"]
 
 [dependencies]
+agent_settings.workspace = true
 anyhow.workspace = true
 askpass.workspace = true
-assistant_settings.workspace = true
 buffer_diff.workspace = true
 chrono.workspace = true
 collections.workspace = true
@@ -56,9 +56,9 @@ time.workspace = true
 time_format.workspace = true
 ui.workspace = true
 util.workspace = true
+workspace-hack.workspace = true
 workspace.workspace = true
 zed_actions.workspace = true
-workspace-hack.workspace = true
 
 [target.'cfg(windows)'.dependencies]
 windows.workspace = true