feat(workflows-sdk,core-flows,medusa,types): add workflow to update promotions to cart (#6474)

what:

- adds API + workflow to add/remove promotions in a cart
- minor fixes in promotions module
- minor type fixes in cart module
- typing fix in workflows-sdk (Thanks @adrien2p)
- fix step result in workflows-sdk (Thanks @adrien2p)

RESOLVES CORE-1768

Co-authored-by: Adrien de Peretti <25098370+adrien2p@users.noreply.github.com>

.changeset/clean-llamas-join.md

@@ -0,0 +1,8 @@
+---
+"@medusajs/workflows-sdk": patch
+"@medusajs/core-flows": patch
+"@medusajs/medusa": patch
+"@medusajs/types": patch
+---
+
+feat(workflows-sdk,core-flows,medusa,types): add workflow to add promotions to cart