Support ISO8601 basic format for DateTime

[fgalan]

(Rasied at telefonicaid/iotagent-json#265 (review))

As described in Orion documentation https://fiware-orion.readthedocs.io/en/master/user/ngsiv2_implementation_notes/index.html#datetime-support, Orion only supports ISO8601 for DateTime.

It should support also de basic format (e.g. 20200222T222222). Otherwise, IOTA date compression plugin will not work.

[fgalan]

Vaguely related with old #1604

[jmcanterafonseca]

In NGSI-LD it is required harmonization of ISO8601 dates to avoid this issue. Please check https://docbox.etsi.org/ISG/CIM/Open/ISG_CIM_NGSI-LD_API_Draft_for_public_review.pdf line 508, clause 4.6.3 Supported data types for Values

-1 to this issue

[fgalan]

This is needed in the southbound interface (i.e. IOTA sending measure to CB) for the NGSIv2. If not implemented, then IOTA compression plugin is not going to work and that part of the integration will break.

In the northbound, regular ISO8601 (the one already supported and I guess the one in 4.6.3 of your cited presentation) will be the one typically used.