assistant: Add term slash command (#13162)

This adds a `term` slash command to the assistant which allows to inject
the latest terminal output into the context.

Release Notes:

- N/A

crates/assistant/src/slash_command.rs

@@ -28,6 +28,7 @@ pub mod prompt_command;
 pub mod rustdoc_command;
 pub mod search_command;
 pub mod tabs_command;
+pub mod term_command;
 
 pub(crate) struct SlashCommandCompletionProvider {
     commands: Arc<SlashCommandRegistry>,