chore(release): use standard PostgreSQL Debian package naming

[aryan-iconic]

What does this PR do?

This updates the Debian package generated by the release workflow to use the standard PostgreSQL extension package naming convention:

postgresql-<version>-jsonschema

For example, the PostgreSQL 18 package is now generated with:

Package: postgresql-18-jsonschema

Changes

• Rename the package identifier from pg-jsonschema to jsonschema.
• Generate Debian package directories using the postgresql-<version>-jsonschema naming convention.
• Update the Debian Package metadata accordingly.
• Update the release artifact pattern to include the generated PostgreSQL extension packages.

Why?

Issue #96 requests a simpler installation experience for pg_jsonschema, similar to:

RUN apt-get update \
    && apt-get install -y --no-install-recommends postgresql-18-cron

The current release workflow already generates Debian packages, but their package metadata does not follow the conventional PostgreSQL extension package naming scheme.

This change makes the generated package suitable for consumption by an APT repository using the conventional package name:

postgresql-18-jsonschema

Scope

This PR updates the Debian packaging produced by the release workflow. It does not itself publish the packages to apt.postgresql.org or another APT repository.

Making the package directly installable with:

apt-get install postgresql-18-jsonschema

would additionally require the generated packages to be published through an APT repository available to the user's PostgreSQL container.

This PR therefore provides the packaging groundwork needed for that installation experience.