docs(alert-sources): describe severity escalation for Netdata and Checkmk

A notification that raises the severity of an open alert opens a new alert at
the higher severity instead of updating the existing one; the recovery closes
both. Downgrades merge into the existing higher-severity alert.

(cherry picked from commit 574aaee)

Author: ysyneu

en/on-call/integration/alert-integration/alert-sources/checkmk.mdx

@@ -115,7 +115,7 @@ You can also send a test from **Test notifications** under **Setup → Events 
 ## Alert Key
 ---
 
-Flashduty computes the Alert Key from the host name `HOSTNAME` and the service name `SERVICEDESC`. Host notifications use an empty service name. Problem, escalation, and recovery notifications for the same host or service carry the same host and service names, so they land on the same alert.
+Flashduty computes the Alert Key from the host name `HOSTNAME` and the service name `SERVICEDESC`. Host notifications use an empty service name. Problem and recovery notifications for the same host or service carry the same host and service names, so they land on the same alert. When the state rises to a higher severity (for example a service going from WARN to CRIT), Flashduty opens a new alert at the higher severity and keeps the earlier alert open; the recovery notification closes both.
 
 Changes to the state, plugin output, notification number, time, host address, site, or labels do not change the Alert Key. Renaming a host or service produces a new alert; close any alert left open under the old name by hand.
 

en/on-call/integration/alert-integration/alert-sources/netdata.mdx

@@ -171,7 +171,7 @@ Netdata sends notifications only for the WARNING, CRITICAL, and CLEAR states.
 | `CRITICAL` | Triggered | Critical |
 | `CLEAR` | Recovered | The severity before recovery (taken from `old_status`) |
 
-When an alert moves between WARNING and CRITICAL, Flashduty updates the severity of the same alert.
+When an alert rises from WARNING to CRITICAL, Flashduty opens a new Critical alert and keeps the Warning alert open. When it drops from CRITICAL to WARNING, the event merges into the existing Critical alert. The CLEAR notification closes both.
 
 Netdata sends CLEAR only when an alert changes from WARNING or CRITICAL to CLEAR.
 

zh/on-call/integration/alert-integration/alert-sources/checkmk.mdx

@@ -115,7 +115,7 @@ chmod +x ~/local/share/check_mk/notifications/flashduty
 ## Alert Key
 ---
 
-Flashduty 用主机名 `HOSTNAME` 加服务名 `SERVICEDESC` 计算 Alert Key；主机通知的服务名为空。同一个主机或服务的问题、状态升级和恢复通知携带相同的主机名和服务名，因此落在同一条告警上。
+Flashduty 用主机名 `HOSTNAME` 加服务名 `SERVICEDESC` 计算 Alert Key；主机通知的服务名为空。同一个主机或服务的问题和恢复通知携带相同的主机名和服务名，因此落在同一条告警上。状态升到更高等级时（例如服务从 WARN 变为 CRIT），Flashduty 会新建一条更高等级的告警，原告警保持触发；恢复通知会同时关闭这两条告警。
 
 状态、插件输出、通知序号、时间、主机地址、站点和标签的变化都不会改变 Alert Key。重命名主机或服务后，新名称会产生新的告警；改名前未恢复的告警需要手动关闭。
 

zh/on-call/integration/alert-integration/alert-sources/netdata.mdx

@@ -171,7 +171,7 @@ Netdata 只对 WARNING、CRITICAL、CLEAR 三种状态发送通知。
 | `CRITICAL` | 触发 | Critical |
 | `CLEAR` | 恢复 | 沿用恢复前的等级（取自 `old_status`） |
 
-告警在 WARNING 和 CRITICAL 之间变化时，Flashduty 会在同一条告警上更新等级。
+告警从 WARNING 升到 CRITICAL 时，Flashduty 会新建一条 Critical 告警，原 Warning 告警保持触发；从 CRITICAL 降到 WARNING 时，事件合并到已有的 Critical 告警。CLEAR 通知会同时关闭这两条告警。
 
 Netdata 只在告警从 WARNING 或 CRITICAL 变为 CLEAR 时发送 CLEAR 通知。