configuration: "flow" parameter for baseline rules and enforcement

[adamdecaf]

Customers Version: v0.5.0

What were you trying to do?
There are several general use-cases for Customers. One such case is a single funding account per namespace/organization that pays out to N Customers/Accounts. This is handy because the funds are always guaranteed to exist in the funding account and payouts require only ReceiveOnly status.

What did you expect to see?
There should be a configuration option to specify this flow: payouts that prevents debiting these Accounts and to never allow changing their status. We only need the one Validated Customer for funding.

[adamdecaf]

Let's add this to GET /configuration/customers as a flow enum.
The first values should be trial (default), payouts, and unrestricted.

[adamdecaf]

cc @joshsadler does this look okay?

[joshsadler]

@adamdecaf I love this.