Config: Replace background.seed_delay and tx.prerun_seed by global prerun_number

The seed_delay for the background noise estimation and the prerun_seed for the error-pattern generation has been replaced by a global prerun_number (best placed directly below master_seed in template.yml), which is set per experiment. See also https://www.3gpp.org/ftp/TSG_SA/WG4_CODEC/3GPP_SA4_AHOC_MTGs/SA4_Audio/Docs/S4aA230065.zip Annex C. This should be reflected in the scripts.

(Note: There is a typo in the description of in the description of C.4.2, where still Q is mentioned - the formula is correct, though)