Databrain and firebolt integration documentation

[rahulpat]

Description

This PR adds comprehensive integration documentation for DataBrain, a modern embedded analytics platform that now supports Firebolt as a data source.

Summary of changes:

• Created new documentation file: docs-mdx/guides/integrations/connecting-to-databrain.mdx
• Updated docs-mdx/docs.json to include DataBrain in the "Integrate with Firebolt" navigation group
• Documentation follows the established structure and style of existing integration guides

Key sections included:

• Overview of DataBrain and benefits of using it with Firebolt
• Prerequisites and requirements
• Step-by-step setup guide (service account creation, role assignment, connection configuration)
• Instructions for building first dashboard
• Real-world use cases (e-commerce, IoT, SaaS, financial reporting)
• Best practices for optimization and performance
• Links to further reading

References:

• DataBrain Firebolt Integration Announcement
• DataBrain Connection Documentation

When should this PR be released to the public?

Immediate release - The DataBrain Firebolt integration is already live and available to users. This documentation can be merged to the gh-pages branch immediately.

[rahulpat]

@lorenzhs