.meta:add-new-system-values for system properties

With the REPO-2243 introduction of using userroles for our default product security configuration, we're hitting a limitation with the logic for .meta:category: system multi-value properties.

The current behavior doesn't 'work' for adding new values to such properties to get them updated on an existing property, as it only will apply the values for non-existing properties.

The new .meta:add-new-values configuration option will fix this as follows:

• only applicable and allowed for .meta:category: system multi-value properties (which are not of type reference or weakreference)
• always needs to be specified together with .meta:category: system and have a or all values provides as well, like:

    foobar:
      .meta:category: system
      .meta:add-new-system-values: true
      value: [foo, bar]

• removing values (compared to the baseline model) will not have any update effect (only will be applied for new/deleted properties)
• when adding new values (compared to the baseline model) only the new values will be applied/added to an existing property (if it doesn't already have those values)

• • if the baseline has values: [a, b]
  • and in the repository this has been modified to: [a,c] 
  • then updating the configuration with values: [b] has no effect
  • or updating the configuration with values: [b,d] results in: [a,c,d] in the repository (only d is added, b is not restored)