Upgrade Cloud SQL for PostgreSQL version

[beyhan]

because version 13 will transition to extended support on February 1, 2026

[stephanme]

PostgreSQL 13 reaches EOL on 2025-11-13 according to https://www.postgresql.org/support/versioning/

Need to update deployment-guide.md as well. I planned to remove PostgreSQL 13 when adding PostgreSQL 17 but, unfortunately, there is no postgres-release (bosh release) yet for v17.

cc: @ZPascal

[ZPascal]

FYI: I also plan to remove PostgreSQL 13 from the Bosh PostgreSQL release in November.