feat(head): add the Request With HEAD keyword and TCs for HEAD success and errors (061_01, 061_02)

New Test Cases for HEAD (TS 104-176 clause 5): on a resource that has GET and HEAD, a HEAD request is answered as the GET would be, without the body, and with 204 No Content on success. Until now the suite did not test HEAD at all.

• 061_01: 204, without Content-Length, on 16 resources: /entities/, /entities/{entityId}, /subscriptions/, /subscriptions/{subscriptionId}, /types/, /types/{type}, /attributes/, /attributes/{attrId}, /temporal/entities/, /temporal/entities/{entityId}, /csourceRegistrations/, /csourceRegistrations/{registrationId}, /csourceSubscriptions/, /csourceSubscriptions/{subscriptionId}, /jsonldContexts/, /jsonldContexts/{contextId}

• 061_02: the same 400 or 404 as the GET (was !338 (merged), merged into this branch)

32 Test Cases in TP/NGSI-LD/CommonBehaviours/CommonResponses/VerifyHEAD/. HEAD is new in TS 104 (GS CIM 009 has none), so every TC is tagged since_ts104_v1.1.1.

Also in the MR:

• the keyword Request With HEAD (resources/ApiUtils/Common.resource): the path after ${NGSI_LD_API_PATH}/, an optional @context for the Link header, every other named argument a URL parameter
• Check Response Headers Not Containing Content-Length (resources/AssertionUtils.resource): a 204 carries no Content-Length (IETF RFC 9110 clause 8.6)
• HEAD in the documentation generator: the verb in doc/analysis/parseapiutilsfile.py, the keyword in requests.py, the directory in generaterobotdata.py

HEAD on the Attribute, the Attribute value and /info/sourceIdentity comes in a later MR, after the TCs of their GET.

What is verified on success is the 204 and the missing Content-Length. The HTTP client does not read a body after a HEAD response, so Check Response Body Is Empty cannot fail on a HEAD; it stays as the statement of the requirement.

Doc unit tests 13/13, statisticsDocumentationData.py 0 of 589 failed, robocop format --check clean, no new unused test data. Against coraine: 32/32.

MRs 2 and 3 of the plan: https://famzang.com/ttf/ngsi-ld-suite-plan.html