Add support for NGSI-LD valueType and more NGSI-LD sub-property types.

[jason-fox]

• Update NGSI-LD processing functionality
• Add tests
• Update documentation.

As defined in the 1.9.1 NGSI-LD specification, there are now two mechanisms available for supporting the equivlent of NGSI-v2 type attribute holding an attribute's datatype.

The following examples show how time values (Date, Time, or DateTime) can be represented in NGSI-LD as reified
Properties. For a reified Property whose value is assigned the JSON type Date, DateTime or Time, one mechanism is to
use the Property's valueType to hold the datatype ("Date", "Datetime" or "Time"), as shown below:

{
  "id": "urn:ngsi-ld:Vehicle:B9211",
  "type": "Vehicle",
  "testedAt": {
    "type": "Property",
    "value": "2018-12-04T12:00:00Z",
    "valueType": "DateTime"
  }
}

Alternatively the data can be a structured to use the JSON-LD @value syntax structure, as shown below:

{
  "id": "urn:ngsi-ld:Vehicle:B9211",
  "type": "Vehicle",
  "testedAt": {
    "type": "Property",
    "value": {
      "@type": "DateTime",
      "@value": "2018-12-04T12:00:00Z"
    }
  }
}

This PR updates NGSI-LD processing to allow for three types of valueType processing to add datatype metadata

• Add nothing
• Add using valueType
• Add using @type

The previous 1.8.1 default (and recommendation) was @type, but this should change since valueType was created to simplify value and make it queriable, The new default (for now) should be nothing, since valueType is not widely supported by context brokers yet.

Note that valueType alwayd optional - it is still possible to define attributes as Property, GeoProperty or Relationship. Furthermore the additional sub-types of Property such as JsonProperty, VocabProperty and ListProperty are also now supported.

[fgalan]

This file (and the rest of similar ones) are under ngsiv2/ structure.

Maybe they are no longer used but we forgot to remove them? In that case, thanks for the clean up :)

[jason-fox]

Remove: autocast (including env var IOTA_AUTOCAST) (#1498) was part of 4.0.0 release

[fgalan]

NTC

[fgalan]

Really needed or a kind of improvement?

[jason-fox]

Moment.js is deprecated, or rather there are better ways of achieving the same result without the use of an unnecessary extra package. In this case Date gives us everything we need from moment.

https://momentjs.com/docs/#/-project-status/

Ideally I'd like to remove both moment and moment-timezone entirely at some point

[fgalan]

Sounds good :) NTC

[fgalan]

LGTM

Let's wait for @AlvaroVega to merge this PR.

[fgalan]

Given that value type is only used by NGSI-LD and taking into account that other LD-related config use the "Ld" token in the name (eg jsonLdContext, maybe it shoulb be named ldValueType?

In that case, the env var could be renamed to IOTA_CB_NGSILD_VALUE_TYPE

[jason-fox]

Fixed b50a691
Moved to IOTA_LD_SUPPORT_DATA_TYPE with config value server.ldSupport.datatype - this aligns to the other LD only config values.

[AlvaroVega]

LGTM

[fgalan]

LGTM