Knf onrboarding new descriptors

Today, while trying to follow the documentation of Section 5.6.5 on how to on-board KNFs, I encountered some issues related to the VNFDs and NSDs of the packages being used as examples. To be more specific, the exemplified packages for the on-boarding of Helm charts and Juju Bundle-based KNFs descriptors were written with SOL005 in mind, and do not work for the new type of descriptors, which follow the SOL006 data model. Therefore, I did some changes to these two subsections, in the scope of this issue.

• For the KNF Helm Chart:

  I have found that this example was already updated in the OSM packages repository, and I found it in https://osm-download.etsi.org/ftp/Packages/examples/. Then, I only need to replace the URLs being used.

• For the KNF Juju Bundle:

  Here, the solution was trickier... As opposed to the previous case, here I did not manage to find the corresponding package in the OSM packages repository. Therefore, I tried to find a similarly simple solution, which also used a Juju bundle. I ended up using the VNFD and NSD for the deployment of Squid proxy, related to Magma Orch from OSM#9 Hackfest.

  Since these packages were not provided, as far as I noticed, in the directory https://osm-download.etsi.org/ftp, I reformulated the example using the links provided by GitLab to download the files corresponding to both packages and added documentation on how to onboard them.