feat(entity-attributes): add TCs for Retrieve Attribute Value (062_02 value only, 062_04 errors)

New Test Cases for Retrieve Attribute Value, GET /entities/{entityId}/attrs/{attrId}/value (TS 104-176 7.6.3.1, TS 104-175 10.4.4). Until now the suite did not test this operation.

• 062_02: the value only representation (TS 104-175 5.4.2), compared as JSON: a String, a Number, a JSON Object and a JSON Array Property, a LanguageProperty (its languageMap), and the same LanguageProperty with lang=fr (the string, 7.2.7)
• 062_04: 400 for an invalid entity id, 404 for an unknown entity, 404 for an unknown attribute

9 Test Cases in TP/NGSI-LD/ContextInformation/Consumption/EntityAttributes/RetrieveAttributeValue/, next to the Retrieve Attribute TCs of !327 (merged). Same conventions as !327 (merged) after its review: since_ts104_v1.1.1, the template argument named as its column, the ProblemDetails title checked in 062_04 and the Content-Type in 062_02.

Also in the MR:

• the keyword Retrieve Entity Attribute Value (resources/ApiUtils/ContextInformationConsumption.resource), sharing Build Entity Attribute Request with Retrieve Entity Attribute
• the check Check Response Body Containing Attribute Value set to (resources/AssertionUtils.resource): the expected value is JSON text, compared as JSON
• the entity sample data/entities/building-value-kinds.jsonld
• the documentation-generator entries (doc/analysis/checks.py, requests.py)
• a robocop format fix on two lines that came with !327 (merged) (b3867de3): the datasetId IF of Build Entity Attribute Request on three lines, the 062_06_02 name

Doc unit tests 12/12, statisticsDocumentationData.py 0 of 578 failed, robocop format --check clean. Against coraine: 9/9.

MR 5 of the plan: https://famzang.com/ttf/ngsi-ld-suite-plan.html