Add disk usage statistics

- add model CustomerPackageDiskUsage for hosting package disk usage
  statistics
- add REST API endpoint for submittings statistics for disk, mysql and
  pgsql usage
- add disk usage information to hosting package detail view
- add separate hosting package disk usage statistic view

gnuviechadmin/hostingpackages/admin.py

@@ -12,6 +12,7 @@ from .models import (
     CustomerHostingPackage,
     CustomerHostingPackageDomain,
     CustomerMailboxOption,
+    CustomerPackageDiskUsage,
     CustomerUserDatabaseOption,
     DiskSpaceOption,
     HostingPackageTemplate,
@@ -95,6 +96,18 @@ class CustomerHostingPackageDomainInline(admin.TabularInline):
     extra = 0
 
 
+class CustomerPackageDiskUsageInline(admin.TabularInline):
+    model = CustomerPackageDiskUsage
+    ordering = ["-used_kb", "source", "item"]
+    fields = ["source", "item", "used_kb"]
+    readonly_fields = ["source", "item", "used_kb"]
+    extra = 0
+    can_delete = False
+
+    def has_add_permission(self, request, obj):
+        return False
+
+
 class CustomerHostingPackageAdmin(admin.ModelAdmin):
     """
     This class implements the admin interface for
@@ -110,6 +123,7 @@ class CustomerHostingPackageAdmin(admin.ModelAdmin):
         CustomerMailboxOptionInline,
         CustomerUserDatabaseOptionInline,
         CustomerHostingPackageDomainInline,
+        CustomerPackageDiskUsageInline,
     ]
     list_display = ["name", "customer", "osuser"]