Use configurable column filters instead of hardcoded ones

[stefanhaerter]

The filter columns which are fetched for dashboard widgets are hardcoded here:

otobo/Kernel/Modules/AgentDashboardCommon.pm

Lines 386 to 389 in 17d808a

	COLUMNNAME:
	for my $ColumnName (
	qw(Owner Responsible State Queue Priority Type Lock Service SLA CustomerID CustomerUserID)
	)

It would make the system more flexible to use filter columns defined in the system configuration, like here:

otobo/Kernel/Modules/AgentDashboardCommon.pm

Lines 609 to 610 in 17d808a

	# get default columns
	my $Columns = $Self->{Config}->{DefaultColumns} || $ConfigObject->Get('DefaultOverviewColumns') || {};