New module: service_catalog: checkout cart, order_now items from service catalog

[tupyy]

SUMMARY

This PR adds a module to checkout cart or order items from service catalog

ISSUE TYPE

• New Module Pull Request

COMPONENT NAME

service_catalog

ADDITIONAL INFORMATION

  - name: Create new mail
      servicenow.itsm.service_catalog:
        action: order_now
        items:
          - sys_id: "{{ result.records[0].sn_items[0].sys_id }}"
            requested_for: abraham.lincoln
            variables:
              new_email: test@example.com

[tupyy]

@mhjacks This PR is on top of the #342 so I'll find files from #342 in this one.
Once #342 is merged I'll rebase it

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