Fix tethys db configure UTF8 encoding error on Windows

[Copilot]

Description

On Windows, PostgreSQL initializes template1 with the OS locale encoding (e.g. WIN1252). createdb -E utf-8 fails because UTF8 is incompatible with a WIN1252-encoded template. The fix is to use template0, which is always encoding-agnostic.

Changes Made to Code

• tethys_cli/db_commands.py: Added --template template0 to the createdb invocation in create_db_user() so database creation succeeds regardless of the server's locale encoding.
• tests/unit_tests/test_tethys_cli/test_db_commands.py: Updated test_db_command_create_db_user to assert --template template0 is passed to createdb.

Related PRs, Issues, and Discussions

• [BUG] tethys db configure fails on Windows w/encoding error #1250

Additional Notes

• template0 is PostgreSQL's pristine, unmodified template and is the recommended approach when specifying a non-default encoding (per PostgreSQL docs and the error hint in the original bug report).

Quality Checks

• At least one new test has been written for new code
• New code has 100% test coverage
• Code has been formatted with Black
• Code has been linted with flake8
• Docstrings for new methods have been added
• The documentation has been updated appropriately

[coveralls]

coverage: 100.0%. remained the same — copilot/fix-issue-1250 into main