Fix date format specifications in BrAPI docs

[bellerbrock]

There are a handful of places where YYYYMMDD date format is specified in the docs (contamination from the MCPD spec documentation) instead of the ISO 8601 standard of yyyy-MM-dd.

@bellerbrock I think this just in the documentation for the examples you gave. OpenAPI uses format 'date' or 'date-time'. All your examples are 'date', which is the format yyyy-MM-dd. Please see https://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.0.3.md#data-types, which is full date in https://datatracker.ietf.org/doc/html/rfc3339#section-5.6. So, the work to do is to correct the description in these examples. Do you have access to make the changes yourself?