Enable setting a user when connecting to PGlite

[pmp-p]

No description provided.

[github-actions]

🚀 Deployed on https://66b21ea7b632b10e31680d34--pglite-dev-demos.netlify.app

[github-actions]

Built bundles:

• Postgres WASM: https://github.com/electric-sql/pglite/actions/runs/10266887362/artifacts/1780956374
• PGlite: https://github.com/electric-sql/pglite/actions/runs/10266887362/artifacts/1780956547
• Interim build files: https://github.com/electric-sql/pglite/actions/runs/10266887362/artifacts/1780956458
• Demos: https://github.com/electric-sql/pglite/actions/runs/10266887362/artifacts/1780956728

[pmp-p]

now after initdb has run ( as WASM_USERNAME default "postgres" ) once it is now possible to drop connexion real user id ( session_user ) and match the privileges to a value set via options.username ( PGUSER ). user has to be created from initial run
eg
CREATE USER test_user WITH PASSWORD 'md5abdbecd56d5fbd2cdaee3d0fa9e4f434';

At the same time is possible to connect to a different options.dbname (PGDATABASE) but only if it has been created before (initial run) and proper rights set.
eg:
CREATE DATABASE test_user WITH OWNER = test_user;
CREATE SCHEMA test_user;