Add field enterprise_users_extensions_marketplace_enabled for groups

Issue: Add Group db field for Enterprise User Extensio... (#474153 - closed)

MR Chain:

1. Add field enterprise_users_extensions_marketpla... (!161728 - merged)
2. Extend extensions gallery metadata with enterpr... (!161740 - merged)
3. Add UI for enterprise user Extension Marketplac... (!161819 - merged)

What does this MR do and why?

Add field enterprise_users_extensions_marketplace_enabled for groups

• Based off existing field in users
• Added to namespace_settings table
• This is needed to support this epic

Changelog: added

MR acceptance checklist

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Related to #474153 (closed)