Add a slash command for automatically retrieving relevant context (#17972)

* [x] put this slash command behind a feature flag until we release
embedding access to the general population
* [x] choose a name for this slash command and name the rust module to
match

Release Notes:

- N/A

---------

Co-authored-by: Jason <jason@zed.dev>
Co-authored-by: Richard <richard@zed.dev>
Co-authored-by: Jason Mancuso <7891333+jvmncs@users.noreply.github.com>
Co-authored-by: Richard Feldman <oss@rtfeldman.com>

crates/assistant/src/slash_command.rs

@@ -18,8 +18,8 @@ use std::{
 };
 use ui::ActiveTheme;
 use workspace::Workspace;
-
 pub mod auto_command;
+pub mod cargo_workspace_command;
 pub mod context_server_command;
 pub mod default_command;
 pub mod delta_command;