FEATURE: Set --notify via creds.json so that preview or push can always notify (#3910)

Either setting these new options OR using --notify on the commandline
will send notification for any specific execution.

Fixes #3906

In a second commit (feel free to remove) I added some logging to
indicate that notifications were enabled or not (useful when testing
each case).

I've manually tested combinations of the various options, for both
preview and push:
 * --notify set or unset on commandline
 * notify_on_* set to "true" or "ASDAS" or "false" or not mentioned
 
All seem to provide the correct logging line - invalid boolean values
are considered false (not an error).
 
I've made an attempt at documentation of the options, not sure if you
want it elsewhere as well.
  
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Author: michaelkaye

commands/ppreviewPush.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"os"
 	"regexp"
+	"strconv"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -210,8 +211,30 @@ func prun(args PPreviewArgs, push bool, interactive bool, out printer.CLI, repor
 		return err
 	}
 
+	var notify = args.Notify
+
+	// We want to notify if args.Notify OR notify_on_*
+	if notifications, ok := providerConfigs["notifications"]; ok && notifications != nil {
+		if push {
+			if notifyOnPush, ok := notifications["notify_on_push"]; ok {
+				if b, _ := strconv.ParseBool(notifyOnPush); b {
+					notify = true
+				}
+			}
+		} else {
+			if notifyOnPreview, ok := notifications["notify_on_preview"]; ok {
+				if b, _ := strconv.ParseBool(notifyOnPreview); b {
+					notify = true
+				}
+			}
+		}
+	}
+	if notify {
+		out.PrintfIf(fullMode, "Notifications are enabled...\n")
+	}
+
 	out.PrintfIf(fullMode, "Creating an in-memory model of 'desired'...\n")
-	notifier, err := PInitializeProviders(cfg, providerConfigs, args.Notify)
+	notifier, err := PInitializeProviders(cfg, providerConfigs, notify)
 	if err != nil {
 		return err
 	}

documentation/advanced-features/notifications.md

@@ -12,6 +12,8 @@ Notifications are configured in the `creds.json` file, since they often contain
   "r53": {},
   "gcloud": {},
   "notifications": {
+    "notify_on_push": false,
+    "notify_on_preview": false,
     "slack_url": "https://api.slack.com/apps/0XXX0X0XX0/incoming-webhooks",
     "teams_url": "https://outlook.office.com/webhook/00000000-0000-0000-0000-000000000000@00000000-0000-0000-0000-000000000000/IncomingWebhook/00000000000000000000000000000000/00000000-0000-0000-0000-000000000000",
     "shoutrrr_url": "discover://token@id"
@@ -22,7 +24,9 @@ Notifications are configured in the `creds.json` file, since they often contain
 
 ## Usage
 
-If you want to send a notification, add the `--notify` flag to the `dnscontrol preview` or `dnscontrol push` commands.
+If you want to send a notification for a specific execution, add the `--notify` flag to the `dnscontrol preview` or `dnscontrol push` commands.
+
+To always send notifications, enable one or more of the `notify_on_push` or `notify_on_preview` options.
 
 Below is an example where we add [the A record](../language-reference/domain-modifiers/A.md) `foo` and display the notification output.