Expressions: Fixes the issue showing expressions editor (#62510)

* Use suggested value for uid

* update the snapshot

* use __expr__

* replace all -100 with __expr__

* update snapshot

* more changes

* revert redundant change

* Use expr.DatasourceUID where it's possible

* generate files

docs/sources/alerting/set-up/provision-alerting-resources/file-provisioning/index.md

@@ -69,7 +69,7 @@ groups:
         #                  evaluation - should be obtained trough the API
         data:
           - refId: A
-            datasourceUid: '-100'
+            datasourceUid: '__expr__'
             model:
               conditions:
                 - evaluator:
@@ -86,7 +86,7 @@ groups:
                   type: query
               datasource:
                 type: __expr__
-                uid: '-100'
+                uid: '__expr__'
               expression: 1==0
               intervalMs: 1000
               maxDataPoints: 43200

docs/sources/alerting/set-up/provision-alerting-resources/terraform-provisioning/index.md

@@ -282,7 +282,7 @@ resource "grafana_rule_group" "my_rule_group" {
 
         // The query was configured to obtain data from the last 60 seconds. Let's alert on the average value of that series using a Reduce stage.
         data {
-            datasource_uid = "-100"
+            datasource_uid = "__expr__"
             // You can also create a rule in the UI, then GET that rule to obtain the JSON.
             // This can be helpful when using more complex reduce expressions.
             model = <<EOT
@@ -298,7 +298,7 @@ EOT
         // Now, let's use a math expression as our threshold.
         // We want to alert when the value of stage "B" above exceeds 70.
         data {
-            datasource_uid = "-100"
+            datasource_uid = "__expr__"
             ref_id = "C"
             relative_time_range {
                 from = 0