[Alerting] fix labels and links in PagerDuty action ui and docs (#64032)

resolves #63222, resolves #63768, resolves #63223

ui changes:

- adds an "(optional)" label after the API URL label
- changes help link to go to alerting docs and not watcher docs
- changes the label "Routing key" to "Integration key" to match other docs
- changes the order of the severity options to match other docs

doc changes:

- changes the reference of "Routing key" to "Integration key" to match other docs
- makes clearer that the API URL is optional

docs/user/alerting/action-types/pagerduty.asciidoc

@@ -92,7 +92,7 @@ section of the alert configuration and selecting *Add new*.
 * Alternatively, create a connector by navigating to *Management* from the {kib} navbar and selecting
 *Alerts and Actions*. Then, select the *Connectors* tab, click the *Create connector* button, and select the PagerDuty option.
 
-. Configure the connector by giving it a name and optionally entering the API URL and Routing Key, or using the defaults.
+. Configure the connector by giving it a name and entering the Integration Key, optionally entering a custom API URL.
 +
 See <<pagerduty-in-pagerduty, In PagerDuty>> for how to obtain the endpoint and key information from PagerDuty and
 <<pagerduty-connector-configuration, Connector configuration>> for more details.
@@ -133,7 +133,7 @@ PagerDuty connectors have the following configuration properties:
 
 Name::      The name of the connector. The name is used to identify a  connector in the management UI connector listing, or in the connector list when configuring an action.
 API URL::   An optional PagerDuty event URL. Defaults to `https://events.pagerduty.com/v2/enqueue`. If you are using the <<action-settings, `xpack.actions.whitelistedHosts`>> setting, make sure the hostname is whitelisted.
-Routing Key::   A 32 character PagerDuty Integration Key for an integration on a service or on a global ruleset.
+Integration Key::   A 32 character PagerDuty Integration Key for an integration on a service, also referred to as the routing key.
 
 [float]
 [[pagerduty-action-configuration]]

x-pack/plugins/triggers_actions_ui/public/application/components/builtin_action_types/pagerduty.tsx

@@ -115,7 +115,7 @@ const PagerDutyActionConnectorFields: React.FunctionComponent<ActionConnectorFie
         label={i18n.translate(
           'xpack.triggersActionsUI.components.builtinActionTypes.pagerDutyAction.apiUrlTextFieldLabel',
           {
-            defaultMessage: 'API URL',
+            defaultMessage: 'API URL (optional)',
           }
         )}
       >
@@ -139,7 +139,7 @@ const PagerDutyActionConnectorFields: React.FunctionComponent<ActionConnectorFie
         fullWidth
         helpText={
           <EuiLink
-            href="https://www.elastic.co/guide/en/elasticsearch/reference/current/actions-pagerduty.html#configuring-pagerduty"
+            href="https://www.elastic.co/guide/en/kibana/current/pagerduty-action-type.html"
             target="_blank"
           >
             <FormattedMessage
@@ -153,7 +153,7 @@ const PagerDutyActionConnectorFields: React.FunctionComponent<ActionConnectorFie
         label={i18n.translate(
           'xpack.triggersActionsUI.components.builtinActionTypes.pagerDutyAction.routingKeyTextFieldLabel',
           {
-            defaultMessage: 'Routing key',
+            defaultMessage: 'Integration key',
           }
         )}
       >
@@ -196,20 +196,20 @@ const PagerDutyParamsFields: React.FunctionComponent<ActionParamsProps<PagerDuty
   } = actionParams;
   const severityOptions = [
     {
-      value: 'info',
+      value: 'critical',
       text: i18n.translate(
-        'xpack.triggersActionsUI.components.builtinActionTypes.pagerDutyAction.severitySelectInfoOptionLabel',
+        'xpack.triggersActionsUI.components.builtinActionTypes.pagerDutyAction.severitySelectCriticalOptionLabel',
         {
-          defaultMessage: 'Info',
+          defaultMessage: 'Critical',
         }
       ),
     },
     {
-      value: 'critical',
+      value: 'error',
       text: i18n.translate(
-        'xpack.triggersActionsUI.components.builtinActionTypes.pagerDutyAction.severitySelectCriticalOptionLabel',
+        'xpack.triggersActionsUI.components.builtinActionTypes.pagerDutyAction.severitySelectErrorOptionLabel',
         {
-          defaultMessage: 'Critical',
+          defaultMessage: 'Error',
         }
       ),
     },
@@ -223,11 +223,11 @@ const PagerDutyParamsFields: React.FunctionComponent<ActionParamsProps<PagerDuty
       ),
     },
     {
-      value: 'error',
+      value: 'info',
       text: i18n.translate(
-        'xpack.triggersActionsUI.components.builtinActionTypes.pagerDutyAction.severitySelectErrorOptionLabel',
+        'xpack.triggersActionsUI.components.builtinActionTypes.pagerDutyAction.severitySelectInfoOptionLabel',
         {
-          defaultMessage: 'Error',
+          defaultMessage: 'Info',
         }
       ),
     },