chore: add directives list to be verbose on plugin order

[toredash]

This PR should make it easier to see how additional plugins can be added to a custom build og nodelocal dnscache.

This addresses some earlier issues where people are not aware on how this is done, as this differs from coredns:
#725
#436

If one look at e.g. #528, #489 or #426, its not clear that this actually works with a single-line change, only because the plugin is/was already included in https://github.com/coredns/coredns/blob/master/plugin.cfg

It's important that the ordering matches, so I used a script to ensure that the correct order is present:

#!/usr/bin/env bash
set -euo pipefail

URL_PLUGIN_CFG="https://raw.githubusercontent.com/coredns/coredns/master/plugin.cfg"
URL_NODE_CACHE="https://raw.githubusercontent.com/kubernetes/dns/master/cmd/node-cache/main.go"

TMP_DIR=$(mktemp -d)

curl -sSL "$URL_PLUGIN_CFG" -o "$TMP_DIR/plugin.cfg"
curl -sSL "$URL_NODE_CACHE" -o "$TMP_DIR/main.go"

# Iterate through defined plugins from coredns/coredns
grep -E '^\w+:\w+.*' "$TMP_DIR/plugin.cfg" | while read -r line; do
    PLUGIN_NAME=$(echo "$line" | cut -d":" -f 1)
    PLUGIN_DIR=$(echo "$line" | cut -d":" -f 2)

    # Check if the plugin package is imported in node-cache main.go
    # Look for the import: _ "github.com/coredns/coredns/plugin/..."
    if grep -q "_ \"github.com/coredns/coredns/plugin/$PLUGIN_DIR\"" "$TMP_DIR/main.go"; then
        # Plugin name is used instead of dir, to handle the case of e.g. prometheus:metrics
        echo "\"$PLUGIN_NAME\","
    fi
done

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This pull-request has been approved by: toredash
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