Create an `env.dart` files passed on the Environment Values passed and prefixed with `flutter_`

run.sh

#!/bin/sh

# list all system env variables starting with flutter_ and put them in an array variable
values=$(env | grep ^flutter_)

# check if values is empty
if [ -z "$values" ]; then
    echo "No environment variables found starting with flutter_"
    exit 0
fi

strippedValues=""
# loop through all values and strip the flutter_ prefix
for value in $values
do
    # strip the prefix
    key=$(echo $value | sed 's/^flutter_//')
    strippedValues="$strippedValues $key"
done
envString=""

# loop through all values and print them
for envVariable in $strippedValues
do
    # split key and value by = (for only the first = in the string)
    key=$(echo $envVariable | cut -d'=' -f1)
    value=$(echo $envVariable | cut -d'=' -f2-)
    
    # check if value is empty
    if [ -z "$value" ]
    then
        echo "No value found for $key"
        exit 0
    fi

    # if key starts with _secret, then it is a secret and should be decoded from base64
    # example _secret_kAPIKey
    if echo "$key" | grep -q '^secret_'; then
        value=$(echo $value | base64 --decode)
        # remove the _secret_ from the key
        key=$(echo $key | sed 's/secret_//')
    fi

    # add the value to the envString
    line="const String $key = '$value';\n"
    envString="$envString$line"
done

# write the envString to the env.dart file
echo "$envString" > $(pwd)/lib/env.dart