Merge preset files

[dapplion]

Preset in defined in multiple files, while the config is defined in one file. I couldn't find a good reason to keep the preset variables split in different files, and this PR should proof that the specs run just fine too. Having all preset variables in a single file should make it a bit simpler to manage them, no need to de-duplicate or parse multiple files.

Merging of the files is done with the script

DIRECTORY=$1
OUTPUT_FILE=$2

FILE_ORDER=("phase0" "altair" "bellatrix" "capella" "deneb" "custody_game" "eip6110" "sharding" "whisk")
for filename in "${FILE_ORDER[@]}"; do
    file_path="$DIRECTORY/$filename.yaml"
    sed -e :a -e '/^\n*$/{$d;N;ba' -e '}' "$file_path" >> $OUTPUT_FILE
    echo -e "\n" >> $OUTPUT_FILE
done

Running two commands from the consensus-specs root dir

bash ../merge_files.sh presets/mainnet presets/mainnet.yaml
bash ../merge_files.sh presets/minimal presets/minimal.yaml

If mantainers want to verify that the merging is consistent and correct, they can run the script locally and check no git diff