Enable GitHub discussions and notifications to mailing lists (#546)

This will enable GitHub discussions and also will send some GitHub
notifications to the project mailing lists as the rest of
implementations.

Author: raulcd

.asf.yaml

@@ -31,6 +31,7 @@ github:
     - julia
   features:
     issues: true
+    discussions: true
   enabled_merge_buttons:
     merge: false
     rebase: true
@@ -39,6 +40,13 @@ github:
     main:
       required_linear_history: true
 
+notifications:
+  commits: [email protected]
+  issues_status: [email protected]
+  issues_comment: [email protected]
+  pullrequests: [email protected]
+  discussions: [email protected]
+
 # publishes the content of the `asf-site` branch to
 # https://arrow.apache.org/julia/
 publish: