Make the stale message for issues more friendly (elastic#31158)

We had some cases when external contributors got very frustrated with
the stale message in old issues. It might sound like we completely
dismiss the effort.

This makes the issue stale message consistent with the message we use
for PRs.

.github/stale.yml

@@ -28,9 +28,18 @@ staleLabel: Stalled
 
 # Comment to post when marking as stale. Set to `false` to disable
 markComment: >
-  This issue has been automatically marked as stale because it has not had
-  recent activity. It will be closed if no further activity occurs. Thank you
-  for your contributions.
+  Hi!
+
+  We just realized that we haven't looked into this issue in a while. We're
+  sorry!
+
+
+  We're labeling this issue as `Stale` to make it hit our filters and
+  make sure we get back to it as soon as possible. In the meantime, it'd
+  be extremely helpful if you could take a look at it as well and confirm its
+  relevance. A simple comment with a nice emoji will be enough `:+1`.
+
+  Thank you for your contribution!
 
 # Comment to post when removing the stale label.
 # unmarkComment: >
@@ -57,13 +66,13 @@ pulls:
     sorry!
 
 
-    We're labeling this issue as `Stale` to make it hit our filters and 
-    make sure we get back to it in as soon as possible. In the meantime, it'd
+    We're labeling this issue as `Stale` to make it hit our filters and
+    make sure we get back to it as soon as possible. In the meantime, it'd
     be extremely helpful if you could take a look at it as well and confirm its
     relevance. A simple comment with a nice emoji will be enough `:+1`.
 
     Thank you for your contribution!
- 
+
   closeComment: >
     Hi!
 
@@ -77,7 +86,6 @@ pulls:
 
     Thank you for your contribution!
 
-
 # issues:
 #   exemptLabels:
 #     - confirmed