Complete documentation of Method status types

[BrechtBonte]

See API documentation: https://docs.mollie.com/reference/v2/methods-api/get-method

The documentation of the different values for the "status" field is a bit ambiguous as it states type is "string" and the value "null" is documented the same as all other statuses. However, we received a response containing "status" => null.

In a strictly typed project this causes errors (which is how we discovered this). This extra documentation should make it clear that this is a valid case.

[sandervanhooft]

Thanks @BrechtBonte ! A bit ambiguous indeed.