Strict OCPP 2.0.1 date-time conformity and validation

[Jared-Newell-Mobility]

OCPP 2.0.1 - Part 2 - Section 2.1.4 Primitive Datatypes

"All time values exchanged between CSMS and Charging Station SHALL be formatted as
defined in [RFC3339]. Additionally fractional seconds have been given an extra limit. The
number of decimal places SHALL NOT exceed the maximum of 3.
Example 1: 2019-04-12T23:20:50.52Z represents 20 minutes and 50.52 seconds after the 23rd
hour of April 12th, 2019 in UTC.
Example 2: 2019-12-19T16:39:57+01:00 represents 39 minutes and 57 seconds after the 16th
hour of December 19th, 2019 with an offset of +01:00 from UTC (Central European Time)"

I think we've to roll our own validation. That should be possible according to the json-schema's docs::

To add a check for a custom format use the FormatChecker.checks decorator.

In addition, all date-time formatting in the library should confirm to the above

[Jared-Newell-Mobility]

original discussion - #216