add device message if quota is exceeding (#2621)

* resultify update_recent_quota()

* add a device-message if quota exceeds QUOTA_WARN_THRESHOLD_PERCENTAGE

* check if a quota warning should be added during housekeeping, this is at least once a day

* dc_get_config("quota_exceeding") is useful for bots

* make clippy happy

* reword QuotaExceedingMsgBody message

* avoid lots of warnings if quota jitters around the warning threshold

* allow clippy::assertions_on_constants

these constants depend on each other, it makes sense to check that they are not changed in an incompatible way

deltachat-ffi/deltachat.h

@@ -377,6 +377,9 @@ int             dc_set_config                (dc_context_t* context, const char*
  *                    an error (no warning as it should be shown to the user) is logged but the attachment is sent anyway.
  * - `sys.config_keys` = get a space-separated list of all config-keys available.
  *                    The config-keys are the keys that can be passed to the parameter `key` of this function.
+ * - `quota_exceeding` = 0: quota is unknown or in normal range;
+ *                    >=80: quota is about to exceed, the value is the concrete percentage,
+ *                    a device message is added when that happens, however, that value may still be interesting for bots.
  *
  * @memberof dc_context_t
  * @param context The context object. For querying system values, this can be NULL.
@@ -5675,6 +5678,13 @@ void dc_event_unref(dc_event_t* event);
 /// Used in message summary text for notifications and chatlist.
 #define DC_STR_FORWARDED                  97
 
+/// "Quota exceeding, already %1$s%% used."
+///
+/// Used as device message text.
+///
+/// `%1$s` will be replaced by the percentage used
+#define DC_STR_QUOTA_EXCEEDING_MSG_BODY   98
+
 /**
  * @}
  */