upgrade postgres

[karenetheridge]

We are currently using postgres 10. Postgres 13 comes out tomorrow; have a look at what new features are available that might be of use to us. Ensure upgrades happen smoothly on production and development infrastructure.

[karenetheridge]

• gen_random_uuid() is now in core; we can drop the pgcrypto extension

[karenetheridge]

Note that conch-backups needs to have its client updated as well (see https://github.com/joyent/buildops-infra/issues/139 for other side effects).