Initialize pgsodium

[lawso017]

Ok probably the last suggestion for a bit... the final step in building a production-grade supabase cluster was enabling "batteries included" pgsodium initialization to support the supabase vault.

My vault operations were initially failing due to lack of a pgsodium master key.

Looking through the codebase didn't show that initialization happening, so I referenced the way Supabase handles this initialization in their dockerized PG (I'm using pg 15):

https://github.com/supabase/postgres/blob/develop/Dockerfile-15

Following their example, this PR initializes a server-managed secret key for the database with a new task, pgsodium.yml.

This task runs after pg_util if pgsodium is in pg_extension_list.

I have tested this on ubuntu 22 for a new cluster, and adding pgsodium to an existing cluster.

I am not sure how long this will be needed because:

https://supabase.com/docs/guides/database/extensions/pgsodium

However, our current vault still requires pgsodium so this was a necessary fix.