NSLCM Statuses are now being offered as an array of Json Nodes

This MR updates the tmf.api to allow for the correct listing of all NSLCM statuses. To this end, we updated the process of adding a new NSLCM status to the list of all status. Before, we were working with string arraylists, which resulted in the incorrect encoding of the JSON NSLCM statuses payloads. Now, we are using the appropriate JSON-appropriate artifacts to manipulate the list of NSLCM statuses and append new statuses. This MR thus fixes the issue of the NSLCM statuses being showned as strings, as it is proven by the image below.

Additionally, the updates were tested with various tests. These can be performed by executing the following command:

docker run -it --rm \
  -v "/home/ubuntu/.m2":/root/.m2 \
  -v "$(pwd)":/opt/maven \
  -w /opt/maven \
  maven:3.9.5-ibm-semeru-17-focal \
  mvn clean verify \
  -Dtest="ServiceRepoServiceTest#testUpdateNSLCMCharacteristicMethodWhenNSLCMValueToUpdateIsNull,ServiceRepoServiceTest#testUpdateNSLCMCharacteristicMethodWhenNSLCMValueToUpdateIsNotNullAndNSLCMDoesntAlreadyExist,ServiceRepoServiceTest#testUpdateNSLCMCharacteristicMethodWhenNSLCMValueToUpdateIsNotNullAndNSLCMAlreadyExists"

Closes #45 (closed)