Update discount messaging

### Description

Change Pro discount message, wherever we use it, from "Save 33% or more on GitLens Pro" to "Save 50% on GitLens Pro" to match current price discounts.

Examples of where this is displayed today:

<img width="502" alt="Image" src="https://github.com/user-attachments/assets/c88cd0f0-b179-4fe4-94e0-6f994fa1d935" />