Add glossary feature documentation to AI translations page

[mintlify]

This PR adds documentation for the new glossary feature in AI translations, which prevents specified terms from being translated. The update includes:

• Explanation of how the glossary works
• Examples of when to use the glossary feature (brand names, product terms, technical jargon)
• The value this provides to users in maintaining brand consistency and technical accuracy
• Clear examples demonstrating the feature's functionality