Include MonitoredPeriod for Device Swap 0.2.0

[jgarciahospital]

Problem description
Device Swap API is a similar API to SIM Swap in its reporting mechanism.

Currently, SIM Swap is supporting a monitoredTime indicator that allows developers to know that a operator cannot report a swap date due to data retention policy or regulatory restriction.

Possible evolution
Proposal is to include same mechanism in Device Swap, as well as aligning the definition and reporting values for this scenario:

- POST retrieve-date: Provides timestamp of latest device swap for a given phone number. If no device swap has been performed, the API will return the first phone number usage in the device (the timestamp of the first time that the phone number was connected to the network, it is, the first time that the SIM is installed in the device) by default. It will return an empty string in case is not possible to retrieve the date (e.g. in case local regulations are preventing the safekeeping of the information for longer than the stated period, or in some edge error cases). In case no data is available in the operators records (e.g. no recorded event), API will return a 422 error.
+ POST retrieve-date: Provides timestamp of latest device swap, if any, for a given phone number.
+      - If no swap has been performed and the network operator supports unlimited DeviceSwap monitoring timeframe, the API will return the first phone number usage in a device (the timestamp of the first time that the phone number was connected to the network, it is, the first time that the SIM is installed in a device).
+      - If the latest device swap date (or the first phone number usage, if no device swap) cannot be communicated due to local regulations (or MNO internal privacy policies) preventing the safekeeping of the information for longer than the stated period, a `null` value will be returned. Optionally, a `monitoredPeriod` could be provided to indicate monitored time frame (in days) supported by the MNO. In this case the response must be treated as "there were no device swap events during 'monitoredPeriod'. Either the parameter is optional, it is recommended to support it in DeviceSwap implementations.