Enhance UX for last_status_change as a datetime

[viniarck]

This capture this discussion:

Enhance UX for last_status_change as a datetime. last_status_change currently stores a epoch value:

❯ http localhost:8181/api/kytos/topology/v3/links | jq -r '.links["cf0f4071be426b3f745027f5d22bc61f8312ae86293c9b28e7e66015607a9260"].metadata'
{
  "last_status_change": 1659109957.997244,
  "last_status_is_active": true
}

Which works great, however since this is a metadata value and exposed in the API, it's not as UX friendly as a formated datetime str for operators, so currently you'd have o keep converting the value from the API, if it were a datetime in the runtime and stored on Mongo as ISODate then it'd be serialized as %Y-%m-%dT%H:%M:%S str in the API response. This breaks compatibility of this field since it's changing its type, but as far as I know and could search in the code base, it doesn't look like it would break any feature, and then we can give a heads up in the changelog for operators in case anyone using the platform that could have been using this field.