postgresqlTestHook: add postgresqlExtraSettings variable

Add `postgresqlExtraSettings` to allow to setup the `postgresql.conf`.
This would be useful in cases where we need to set
`shared_preload_libraries`.

doc/hooks/postgresql-test-hook.section.md

@@ -45,6 +45,7 @@ Bash-only variables:
  - `postgresqlTestSetupCommands`: bash commands to run after database start, defaults to running `$postgresqlTestSetupSQL` as database administrator.
  - `postgresqlEnableTCP`: set to `1` to enable TCP listening. Flaky; not recommended.
  - `postgresqlStartCommands`: defaults to `pg_ctl start`.
+ - `postgresqlExtraSettings`: Additional configuration to add to `postgresql.conf`
 
 ## Hooks {#sec-postgresqlTestHook-hooks}
 

pkgs/build-support/setup-hooks/postgresql-test-hook/postgresql-test-hook.sh

@@ -56,6 +56,8 @@ EOF
   echo 'initializing postgresql'
   initdb -U postgres
 
+  echo "$postgresqlExtraSettings" >>"$PGDATA/postgresql.conf"
+
   # Move the socket
   echo "unix_socket_directories = '$NIX_BUILD_TOP/run/postgresql'" >>"$PGDATA/postgresql.conf"