SqlRS: Make DatabaseServerName and DatabaseInstanceName as non-mandatory

Details of the scenario you tried and the problem that is occurring:
Today if the SqlRS resource is used to change properties that does not necessarily need the properties
DatabaseServerName and DatabaseInstanceName, they still need to be specified.

    [Required, Description("Name of the SQL Server to host the Reporting Service database.")] String DatabaseServerName;
    [Required, Description("Name of the SQL Server instance to host the Reporting Service database.")] String DatabaseInstanceName;

I suggest we look at making these properties non-mandatory. And if the Reporting Services is not initialized, the resource throws an error saying that it's missing the DatabaseServerName and DatabaseInstanceName to properly initialize the Reporting Services.

The DSC configuration that is using the resource (as detailed as possible):

SqlRS DefaultConfiguration
{
    InstanceName                 = 'MSSQLSERVER'
    ReportServerReservedUrl      = @('https://+:443')
    ReportsReservedUrl           = @('https://+:443')
    UseSsl                       = $true
}

Version of the Operating System, SQL Server and PowerShell the DSC Target Node is running:
All

What module (SqlServer or SQLPS) and which version of the module the DSC Target Node is running:
n/a

Version of the DSC module you're using, or 'dev' if you're using current dev branch:
Dev

Start at the SqlRS resource definition and the validation for DatabaseServerName and DatabaseInstanceName. Use the supplied PowerShell configuration to verify that unrelated property changes no longer require those values, while an uninitialized Reporting Services setup still reports both missing values.