[github-actions]Update version.py to v2.2.0

- Document PostgreSQL 15+ as supported backend alongside MySQL 8+
- Add PostgreSQL environment variables (DJ_PG_HOST, DJ_PG_PORT, etc.)
- Document backend-parameterized tests and how to run per-backend
- Show pip install with [postgres] extra for psycopg2-binary
- Add PostgreSQL to external containers instructions

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Relative link works on GitHub but breaks on PyPI, which renders
the README without access to other repo files.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Add database.dbname config option (env: DJ_DBNAME) to specify which
PostgreSQL database to connect to. Defaults to 'postgres' if not set
(existing behavior preserved).

Required where the primary database has a non-default name.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

…nit__, add tests

- Extract duplicated connect kwargs construction into _build_connect_kwargs()
- Add dbname as explicit keyword argument to Connection.__init__() for
  programmatic use (explicit arg overrides config value)
- Add 5 unit tests for dbname settings (default, env var, config file,
  dict access, override context manager)
- Bump version to 2.2.1

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

…database_prefix

Review feedback from PR #1426:

1. Rename setting to database.name (env: DJ_DATABASE_NAME) to match
   section naming style and avoid stutter. Connection kwarg is
   database_name. Adapter still receives dbname (psycopg2's parameter).

2. Deprecate database_prefix — emit DeprecationWarning when non-empty.
   Will be removed in DataJoint 2.3. database.name is the replacement.

3. Revert version.py to 2.2.0 — release workflow owns version bumps.

4. Warn when database.name is set with MySQL backend (MySQL does not
   support database selection via this parameter).

5. Include database name in Connection.__repr__ and log message when set.
   Format: user@host:port/database_name

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Fix CONTRIBUTING.md link for PyPI

Move the DeprecationWarning from Pydantic model validator (fires at
config load time with unhelpful stacklevel) to Schema.activate() where
database_prefix is consumed. The warning now points to the user's
dj.Schema(...) call — exactly where they need to make a change.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

feat: add database.dbname setting for PostgreSQL connections