The `::set-output` command has been deprecated and is scheduled for
removal on Jun 1, 2023 [1]. The recommended way to set output parameters
today is by writing them to `$GITHUB_OUTPUT` file [2].

[1] https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/
[2] https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#setting-an-output-parameter

Resolves: #6

Use `$GITHUB_OUTPUT` instead of `::set-output`

The 'setup-postgres' action used to create a superuser that hasn't been
exposed to users via 'connection-uri' output. The superuser has been
named after GitHub Action's system user (i.e. 'runner'), had no password
and could have been used via PostgreSQL client applications [1] or when
using manually constructed connection URI with no user set.

The user set via action's input parameters used to be unprivileged with
escalated permissions to create databases on-demand. I don't remember
why I made things this way, maybe I got confused somewhere along the
way, but I don't think having both private superuser and public
unprivileged user is a good idea. It's quite common in tests to
dynamically create databases and/or users for applications under test,
thus superuser permissions are required.

This patch removes a private superuser named after the GitHub Action's
system user (i.e. 'runner') in favor of granting superuser permissions
to a user set via action's input parameters. Those who explicitly relied
on 'runner' user might got affected as the user WON'T exist anymore.

[1] https://www.postgresql.org/docs/15/reference-client.html

BREAKING CHANGE: create superuser

It turns out that PostgreSQL comes with weird default that allows
passwordless authentication for localhost connections [1]. This
essentially means that 'password' input parameter for this action was
ignored.

The 'setup-postgres' action's primary use case is to be used on CI where
most of the time authentication is desired in order to verify that
passwords are passed correctly from applications under test.

This patch enforces password authentication even for localhost
connections, making sure that passwords are verified and not ignored.
This will break everyone who previously passed wrong password or didn't
pass it at all.

[1] https://www.postgresql.org/docs/15/auth-trust.html

Fixes: #5

BREAKING CHANGE: enforce password authentication

The 'setup-postgres' action used to set libpq environment variables [1]
with connection parameters so the PostgreSQL client applications [2],
such as 'psql' or 'createuser', won't require any configuration before
using.

Unfortunately these libpq environment variables are also used by all
libpq clients including database drivers such as 'psycopg'. While this
may sound good, it may as well lead to undesired behaviour and unobvious
issues when connection parameters are automatically pulled from
environment but most not.

Nevertheless, the need to easy usage of the client applications [2] is
indisputable because providing a bunch of connection parameters all the
time is tedious. Therefore this patch pushes requires connection
parameters to the connection service file [3], so the client
applications can pull the data on-demand. E.g:

    $ psql service=superuser -c "SELECT 1;"
    $ PGSERVICE=superuser createuser myuser

[1] https://www.postgresql.org/docs/15/libpq-envars.html
[2] https://www.postgresql.org/docs/15/reference-client.html
[3] https://www.postgresql.org/docs/15/libpq-pgservice.html

BREAKING CHANGE: don't set connection env vars