Add optional poolConfig to Postgres session options

[thosakwe]

WHY are these changes introduced?

When using PostgreSQL for sessions, it's not possible to use a host that requires a specific SSL certificate.

For example, DigitalOcean managed databases come with a CA certificate needed for authentication.

The reason you can't use these hosts is because the PostgreSQLSessionStorage constructor has no way to provide SSL options.

WHAT is this pull request doing?

I added an optional pg.PoolConfig option.

Type of change

• Minor: New feature (non-breaking change which adds functionality)

Checklist

• I have used yarn changeset to create a draft changelog entry (do NOT update the CHANGELOG.md files manually)
• I have added/updated tests for this change (no existing tests needed modification)
• I have documented new APIs/updated the documentation for modified APIs (for public APIs)

[thosakwe]

I'm actually not sure this is necessary.

It turns out that pg accepts the same environment variables as libpq and psql:

node-postgres uses the same environment variables as libpq and psql to connect to a PostgreSQL server. Both individual clients & pools will use these environment variables.

https://node-postgres.com/features/connecting

So in my case, I could export PGSSLMODE=require and PGSSLROOTCERT=<.ca file path>

If this PR turns out to not be necessary, that's okay, this post will at least be on the Internet to help the next person who has this problem.