Fix package configuration to include Jinja2 template files

- Add package-data configuration to include *.j2 files
- This ensures prompt templates are included in the package distribution
- Fixes missing system_prompt.j2 error when using CodeActAgent

Co-authored-by: openhands <openhands@all-hands.dev>

Author: openhands-agent

openhands/core/pyproject.toml

@@ -20,3 +20,6 @@ build-backend = "setuptools.build_meta"
 where = ["../.."]
 include = ["openhands*"]
 
+[tool.setuptools.package-data]
+"*" = ["*.j2"]
+