This pull request adds the release-please-core workflow and
configuration files. The release-please workflow is triggered on push to
the main branch and on manual workflow dispatch. It sets up Python,
installs Poetry, configures Poetry, and runs release-please for the
backend/core package. The release-please configuration file specifies
the release type, package name, bump patch for minor pre-major,
changelog notes type, include v in tag, tag separator, and component.