[WIP] PyPI-publishable connectors_service

[lorenabalan]

Related to https://github.com/elastic/search-team/issues/10999

• Added new pipeline for publishing to PyPI: .buildkite/pypi-publish-pipeline.yml
• Renamed app/connectors_service/connectors to app/connectors_service/connectors_service
• Incorporated pytest, pyright, and ruff config into pyproject.toml
• Fixed .buildkite/run_notice_check.sh for the new folder structure when there's a change in any NOTICE.txt

Checklists

Pre-Review Checklist

• this PR does NOT contain credentials of any kind, such as API keys or username/passwords (double check config.yml.example)
• this PR has a meaningful title
• this PR links to all relevant github issues that it fixes or partially addresses
• if there is no GH issue, please create it. Each PR should have a link to an issue
• this PR has a thorough description
• Covered the changes with automated tests
• Tested the changes locally
• Added a label for each target release version (example: v7.13.2, v7.14.0, v8.0.0)
• For bugfixes: backport safely to all minor branches still receiving patch releases
• Considered corresponding documentation changes
• Contributed any configuration settings changes to the configuration reference
• if you added or changed Rich Configurable Fields for a Native Connector, you made a corresponding PR in Kibana

Changes Requiring Extra Attention

• Security-related changes (encryption, TLS, SSRF, etc)
• New external service dependencies added.

Related Pull Requests

Release Note

[lorenabalan]

Closing this in favour of #3748 - renaming the package is heavy and technically we can get away without it for now. It's just that it's a slightly surprising folder structure.