Rename labelnamespaces variable to ignoreNamespaces

[draychev]

The variable name labelnamespaces does not provide enough context around what and why.
I propose we rename labelnamespaces to ignoreNamespaces, which will match the original store of value and most importantly will carry more context.

This needs to be renamed in a few places:

• osm-azure/charts/osm-arc/templates/osm-label.yml

  Line 126 in a317fec

  - name: labelnamespaces

• osm-azure/charts/osm-arc/templates/osm-label.yml

  Lines 138 to 139 in a317fec

  	namespaces=${labelnamespaces}
  	for namespace in ${namespaces}

https://github.com/Azure/osm-azure/search?q=labelnamespaces

[draychev]

Related issue: #110