Update serverless status to unavailable in graph docs (#3162)

Rel: elastic/docs-content-internal#357

Author: florent-leborgne

explore-analyze/visualize/graph.md

@@ -3,7 +3,7 @@ mapped_pages:
   - https://www.elastic.co/guide/en/kibana/current/xpack-graph.html
 applies_to:
   stack: ga
-  serverless: ga
+  serverless: unavailable
 products:
   - id: kibana
 ---

explore-analyze/visualize/graph/graph-configuration.md

@@ -3,7 +3,7 @@ mapped_pages:
   - https://www.elastic.co/guide/en/kibana/current/graph-configuration.html
 applies_to:
   stack: ga
-  serverless: ga
+  serverless: unavailable
 products:
   - id: kibana
 ---

explore-analyze/visualize/graph/graph-troubleshooting.md

@@ -4,7 +4,7 @@ mapped_pages:
   - https://www.elastic.co/guide/en/kibana/current/graph-troubleshooting.html
 applies_to:
   stack: ga
-  serverless: ga
+  serverless: unavailable
 products:
   - id: kibana
 ---

troubleshoot/kibana/graph.md

@@ -4,7 +4,7 @@ mapped_pages:
   - https://www.elastic.co/guide/en/kibana/current/graph-troubleshooting.html
 applies_to:
   stack: all
-  serverless: all
+  serverless: unavailable
 products:
   - id: kibana
 ---