pg_walsummary: add page (#18485)

Co-authored-by: Managor <42655600+Managor@users.noreply.github.com>

pages/common/pg_walsummary.md

@@ -0,0 +1,16 @@
+# pg_walsummary
+
+> Print contents of WAL summary files.
+> More information: <https://www.postgresql.org/docs/current/app-pgwalsummary.html>.
+
+- Convert a WAL summary file to text:
+
+`pg_walsummary {{path/to/file}}`
+
+- Print one line per individual modified block (rather than ranges):
+
+`pg_walsummary {{[-i|--individual]}} {{path/to/file}}`
+
+- Suppress normal output (only errors):
+
+`pg_walsummary {{[-q|--quiet]}} {{path/to/file}}`