Option to disable empty-variable rule for VAR and leave it for *** Variables *** section

[borutzki]

Since new VAR syntax has by default the same settings as creating empty variables in *** Variables *** section, it is inconsistent with old Create Dictionary / Create List / Set Variable keywords that allowed creating empty variables with no need to use placeholders.

For example, this:

&{some_dict}    Create Dictionary  # no issues

with VAR and default for empty-variable rule is suggested to be refactored into this:

VAR    &{some_dict}    # now Robocop will complain

It seems inconsistent with previous way of creating empty variables inside of keywords. Maybe that suggestion is not necessarily bad but it would be nice-to-have feature to separate the setting for Variables section and for inline-created VARs.