NSLifecycleManagement-API.NSLCMOccurences.robot small bugs 2.6.1

https://forge.etsi.org/rep/nfv/api-tests/blob/2.6.1-fix-plu/SOL005/NSLifecycleManagement-API/NSLCMOccurences.robot

Attribute of NsLcmOpOcc 'operationParams' has cardinality [0-1], so it shouldn't be a required property. Proof https://www.etsi.org/deliver/etsi_gs/NFV-SOL/001_099/005/02.06.01_60/gs_nfv-sol005v020601p.pdf

GET status information about multiple NS LCM occurrences with "exc... | FAIL |
ValidationError: Validation error for schema NsLcmOpOccs.schema.json: 'operationParams' is a required property

GET status information about multiple NS LCM occurrences with "fie... | FAIL |
ValidationError: Validation error for schema NsLcmOpOccs.schema.json: 'operationParams' is a required property

GET status information about multiple NS LCM occurrences with "exc... | FAIL |
ValidationError: Validation error for schema NsLcmOpOccs.schema.json: 'operationParams' is a required property

GET status information about multiple NS LCM occurrences with "all... | FAIL |
ValidationError: Validation error for schema NsLcmOpOccs.schema.json: 'operationParams' is a required property

Schemas that should be modified:

schemas/NsLcmOpOcc.schema.json
schemas/NsLcmOpOccs.schema.json

GET information about multiple NS instances as Paged Response :: T... | FAIL |
Resolving variable '${response.headers}' failed: AttributeError: 'dict' object has no attribute 'headers'