I have GeoServer hosted on my server and I want to connect a store so that I can serve layers from there. I am aware that I can connect external WMS source to geoserver, but not sure how to connect TMS.
Currently, you can only cascade WMS and WMTS services. TMS is an old and not very well supported "standard" so there is no easy way to discover the extents and number of tiles.
It would be possible to extend the existing WMTS cascading code to support TMS but it would require some coding or sponsorship to make it happen.