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/Cargo.toml

@@ -55,6 +55,7 @@ smol.workspace = true
 strsim = "0.11"
 strum.workspace = true
 telemetry_events.workspace = true
+terminal_view.workspace = true
 theme.workspace = true
 tiktoken-rs.workspace = true
 toml.workspace = true