Adapting fast pixel clustering version to allow 8-cell connectivity (ATLIDTRKCP-240)

This merge request includes changes to the pixel clusterisation tool to adapt the fast clusterisation method to use connected component analysis based on 4-cell or 8-cell connectivity, depending on the configuration. By default, it uses 8-cells to preserve the output cluster collection. The old function is now removed and replaced with the new one.

I have also removed unused property from the tool and its configuration.