In order to utilize IT Partner Gateways admin API for account cleanup, we will need to store the azure customer ID on both the subscriptions and contracts tables' billing_provider_id columns. The API will accept AzureCustomerId and OfferId(already saved). This data is in the response from partner gateway and should be stored during contract creation.

Done:
azureCustomerId is found in the billing_provider_id field of  GET /api/swatch-contracts/internal/contracts endpoint. The format will be 

AzureResourceId;AzurePlanId;AzureOfferId;AzureCustomerId