Create tenant init API

There is a need to create initial groups for a new tenant in prod environment. Apart from initial groups, service principal user should be created and added as owner to a number of groups. To handle that, please create a tenant init API in entitlements service.

Once the infrastructure is ready for a new tenant, this API gets called. This API should be called with a service user principal's jwt token. A service principal user is the one, whose username is set in app-dev-sp-username secret in keyvault. data-partition-id header is required, it will tell the service for which tenant initial groups need to be created. The API has an idempotent characteristic: no matter how many times you call it, initial groups for tenant will be created only once.