converted html to a boolean and updated documentation and schema

docs/how-to/monitor-your-backups.md

@@ -333,7 +333,7 @@ pushover:
         message: "Backup <b>Started</b>"
         priority: -2
         title: "Backup Started"
-        html: 1
+        html: True
         ttl: 10  # Message will be deleted after 10 seconds.
     fail:
         message: "Backup <font color='#ff6961'>Failed</font>"
@@ -342,7 +342,7 @@ pushover:
         retry: 30  # Used only for priority 2. Default is 30 seconds.
         device: "pixel8"
         title: "Backup Failed"
-        html: 1
+        html: True
         sound: "siren"
         url: "https://ticketing-system.example.com/login"
         url_title: "Login to ticketing system"
@@ -350,7 +350,7 @@ pushover:
         message: "Backup <font color='#77dd77'>Finished</font>"
         priority: 0
         title: "Backup Finished"
-        html: 1
+        html: True
         ttl: 60
         url: "https://ticketing-system.example.com/login"
         url_title: "Login to ticketing system"