New-DcnImage: Properly record database size from backup files

[lowlydba]

If the database image is being created from a backup that already exists, the function defaults to a size of 1MB:

dbaclone/functions/image/New-DcnImage.ps1

Lines 347 to 352 in 2d73971

	else {
	$DatabaseCollection = @{
	Name = $Database
	Size = 1
	};
	}

The size could be grabbed from the restored version of the database in either case (new backup or existing) after any provided SQL scripts are run against it to provide a more accurate size value when logging it to the metadata store.

This value is also used (pre-restore) to check size requirements, but could probably be replaced with the backup size (via Read-DbaBackupHeader?) as a fallback, which would be more accurate than 1:

dbaclone/functions/image/New-DcnImage.ps1

Lines 387 to 402 in 2d73971

	if ($PSCmdlet.ShouldProcess($db, "Checking available disk space for database")) {
	# Check the database size to the available disk space
	if ($computer.IsLocalhost) {
	$availableMB = (Get-PSDrive -Name $ImageLocalPath.Substring(0, 1)).Free / 1MB
	}
	else {
	$command = [ScriptBlock]::Create("(Get-PSDrive -Name $($ImageLocalPath.Substring(0, 1)) ).Free / 1MB")
	$availableMB = Invoke-PSFCommand -ComputerName $computer -ScriptBlock $commandGetLocalPath -Credential $DestinationCredential
	}
	$dbSizeMB = $db.Size
	if ($availableMB -lt $dbSizeMB) {
	Stop-PSFFunction -Message "Size of database $($db.Name) does not fit within the image local path" -Target $db -Continue
	}
	}

[lowlydba]

May need to be on hold until dataplat/dbatools#8302 is fixed

[lowlydba]

I'll see about getting a PR for this soon now that the upstream issue is resolved, should be easy now that we're capturing the restore header info already from #184