Add ability to disable link based attachment migration

[alexey-nenazhenko-bm]

Motivation

When the --attachments parameter is not supplied AssetMigration.MigrateValue is trying to find and migrate attachment if it's link was found in document field value. Sometimes attachments might be missing, but referenced from RTE field for example. It will be very helpful to have a setting disabling this default behavior.

Proposed solution

1. Add "IgnoreAttachmentLinks" app setting
2. Add setting to ToolConfiguration
3. Change method code this way:

if (mediaLinkKind == MediaLinkKind.Path)
{
    // path needs to be converted to GUID
    if (mediaKind == MediaKind.Attachment && path != null)
    {
        if (configuration.IgnoreAttachmentLinks)
        {
            logger.LogTrace("'{FieldName}' Skipped Match={Value}", fieldName, result);
        }
        else
        {
            switch (await attachmentMigrator.TryMigrateAttachmentByPath(path, $"__{fieldName}"))
            {
                case MigrateAttachmentResultMediaFile(true, _, var x, _):
                {
                    mfis = [new AssetRelatedItem { Identifier = x.FileGUID, Dimensions = new AssetDimensions { Height = x.FileImageHeight, Width = x.FileImageWidth }, Name = x.FileName, Size = x.FileSize }];
                    hasMigratedAsset = true;
                    logger.LogTrace("'{FieldName}' migrated Match={Value}", fieldName, result);
                    break;
                }
                case MigrateAttachmentResultContentItem { Success: true, ContentItemGuid: { } contentItemGuid }:
                {
                    mfis =
                    [
                        new ContentItemReference { Identifier = contentItemGuid }
                    ];
                    hasMigratedAsset = true;
                    logger.LogTrace("'{FieldName}' migrated Match={Value}", fieldName, result);
                    break;
                }
                default:
                {
                    logger.LogTrace("Unsuccessful attachment migration '{Field}': '{Value}' - {Match}", fieldName, path, result);
                    break;
                }
            }
        }
    }

    if (mediaKind == MediaKind.MediaFile)
    {
        logger.LogTrace("'{FieldName}' Skipped Match={Value}", fieldName, result);
    }
}