startkde: Use the sound theme setting for startup sound
Even if we're not doing a full compliant sound name resolution, this will work for virtually every theme out there until a full port to canberra.
Otherwise the startup sound will be harcoded to ocean
.
Targeting 6.0 directly, as !4072 (merged) already covers this from 6.1 on. I ended up blatantly copying the exact lines from that MR to reduce the differences between branches.
Edited by Ismael Asensio