Update "Contact Sales" link for Duo Pro add-on

What does this MR do and why?

Resolves https://gitlab.com/gitlab-org/gitlab/-/issues/435195+.

Updates the "Contact Sales" link for the Duo Pro add-on copy, in the "Introducing Duo Pro" introduction blurb and the "not enough seats" error. The link should change from /sales to /solutions/code-suggestions/sales.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Scenario	Location	Screenshot	Testing Patch
"Introducing Duo Pro" introduction	"Contact Sales" button		show_intro.patch
"Not enough seats" error	Link in error description		sm_no_seats_error.patch

How to set up and validate locally

Same validation steps as here: !141381 (merged). But instead, we just want to validate the links are as expected.