CE psd update

The noise curve present in Bilby for Cosmic Explorer is outdated. Moreover, to correct for effects due to the detector size a particular position of the source is assumed. So the ASDs/PSDs are not exactly correct for arbitrary sources. This commit fixes this by using the latest displacement ASDs and dividing it by the length of the detector. Note at high frequencies appropriate detector size effects have to be computed. The 40km CE is placed at the Hanford site and the 20km one is at the Livingston site. Also, ASDs for the low frequency optimized 40km detector and post-merger optimized 20km detector are added.