Create a marketplace / CRM integration

Create a new marketplace or CRM integration.

Supported providers:

• AWS_MARKETPLACE - AWS Marketplace Metering Service
• AZURE_MARKETPLACE - Azure Marketplace SaaS metering
• GCP_MARKETPLACE - GCP Cloud Commerce / Service Control
• STRIPE - Stripe Billing Meter Events
• SALESFORCE - Salesforce CRM (custom usage object)
• METRONOME - Metronome usage ingestion

Secret config fields are encrypted at rest and never returned on read.

Requires a secret key (sk_*) with the ADMIN role.