Introduce staff-only inline completion provider (#21739)

Release Notes:

- N/A

---------

Co-authored-by: Thorsten Ball <mrnugget@gmail.com>
Co-authored-by: Bennet <bennet@zed.dev>
Co-authored-by: Thorsten <thorsten@zed.dev>

crates/inline_completion_button/Cargo.toml

@@ -16,6 +16,7 @@ doctest = false
 anyhow.workspace = true
 copilot.workspace = true
 editor.workspace = true
+feature_flags.workspace = true
 fs.workspace = true
 gpui.workspace = true
 language.workspace = true
@@ -25,6 +26,7 @@ supermaven.workspace = true
 ui.workspace = true
 workspace.workspace = true
 zed_actions.workspace = true
+zeta.workspace = true
 
 [dev-dependencies]
 copilot = { workspace = true, features = ["test-support"] }