startedAt y expiredAt do not follow date-time format

[jlurien]

Problem description
Currently the properties in SesssionInfo startedAt and expiresAt are defined as "in seconds since Unix epoch", but this is very excepcional in CAMARA as all other time properties have format date-time, following RFC 3339.

Commonalities do not explicitly mandate to follow date-time format for time values, only to add reference to RFC 3339 if used, but it may require some more explicit guideline for this.

Expected behavior

Is this intentional or should we adopt date-time as well, which is more friendly for humans.

[eric-murray]

Happy to move to date-time format, but would like seconds to continue to be constrained to an integer, as fractional seconds would be excessive precision for this use case.

[hdamker]

QoD Call on April 19th: Agreed to be done in scope of v0.11.0.

[tanjadegroot]

the common data types from commonalities has StartDate and EndDate types of type date-time, so I think the both name and type of the schema(s) in qod should be aligned to the common ones. Other types may also need to be checked.
btw the DeviceStatus has a similar schema called "startsAt" that also should be aligned to common schema.

[hdamker]

Fixed in #296