feat(api): add option to remove Novu branding in the inbox

[ChmaraX]

What changed? Why was the change needed?

Added option to remove Novu branding from Inbox component for paid customers.

• Only non-free tiers are able to update this setting
• After customer is set back to free, this setting is set back to false
• Value will be always false unless explicitly set to true on integration entity
• This setting is exposed for Inbox component inside session
• This feature is under a feature flag IS_IMPROVED_BILLING_ENABLED

Related PRs: https://github.com/novuhq/novu/pull/6500 https://github.com/novuhq/packages-enterprise/pull/218

[linear[bot]]

PLAT-52 Display "Remove Novu branding" toggle in In-App integrations panel