Add extra dimensions which are not pyramided

[felixcremer]

This does for example happen when we have RGB images in a geotiff and we have overviews which we would like to have for plotting but we only have red green and blue band.
Then we still want to have the pyramid levels in the x and y dimensions and we would like to load all three bands simultaneously.

[felixcremer]

This is described as an extension at the TileMatrixSet definition see https://docs.ogc.org/is/17-083r4/17-083r4.html#toc85.
Doing it according to the TMS definition has the benefit of being compliant to geozarr.