Define a schema valid for both startPeriod and endPeriod

[ioggstream]

I expect

To define a reusable schema valid for both startPeriod and endPeriod

components:
  schemas:
    SDMXPeriod:
       type: string
       pattern: '^\d{4}-?((\d{2}(-\d{2})?)|A1|S[1|2]|Q[1-4]|T[1-3]|M(0[1-9]|1[0-2])|W(0[1-9]|[1-4][0-9]|5[0-3])|D(0[0-9][1-9]|[1-2][0-9][0-9]|3[0-5][0-9]|36[0-6]))?$'
       description: |-
          Examples:
          * `2000`: Year (ISO 8601)
          * `2000-01`: Month (ISO 8601)
          * `2000-01-01`: Date (ISO 8601)
          * `2000-Q1`: Quarter (SDMX)
          * `2000-W01`: Week (SDMX)



startPeriod:
      in: query
      name: startPeriod
      description: |
        The start of the period for which results should be supplied (inclusive).
      schema:
         $ref: '#/components/schemas/SDMXPeriod'