Postgresql Event store implementation

Eventstore implementation to store events in Postgresql

Running tests

The tests expect a local Postgresql to be running. It uses the standard libpq environment variables to find it. You will
need permissions to create schemas (namespaces) in the database that is connected to.

$3

In a terminal window, run:

``shell
docker run --rm -it -p 5432:5432 -e POSTGRES_HOST_AUTH_METHOD=trust postgres:14-alpine
`

This runs a PostgreSQL on port 5432 (the default), with password authentication disabled
(which is reasonable for local testing). The database is created with a default "postgres"
user and database, so you still need to specify this when running tests:

`shell
PGUSER=postgres yarn test
`

#### Environment variables

The most important variables:

| Name | Description |
|------------|:---------------------------------------------------------------------|
| PGUSER | User name |
| PGPASSWORD | Password |
| PGHOST | Server host |
| PGPORT | Server port |
| PGDATABASE | Database within server to connect to (defaults to same as user name) |

The full list is at https://www.postgresql.org/docs/current/libpq-envars.html

$3

The library includes a helper for connecting to an AWS RDS instance with IAM auth. In order to run the test for this,
you need to set two additional environment variables:

| Name | Description |
|------------|:---------------------------------------------------------------------|
| AWS_REGION | AWS region of an RDS database for testing |
| AWS_URL | URL of RDS database: pg://user@hostname/database |

By contrast, these tests are not run if the environment variables are not set.

Releasing a new version

`shell
yarn version --patch
git push --tags origin main
``