[Compute usage quotas] Allow unlimited quota for individual accounts

[jnywong]

Context

There are times when we want to allow unrestricted access to resources to certain user accounts, such as the deployment-service-check for 2i2c infra

Definition of Done

• Define specification for such a quota policy
• Update traitlets configuration
• Update usage quota manager logic
• Validate with a test deployment on staging hub
• Write unit tests
• Update documentation