[INTPROD-9639] Add reaction payload type support

[david-lyft]

• Modified message_router to support reaction payload types
• Updated python version as 3.8 is no longer supported in the setup environment

[Copilot]

Pull Request Overview

This PR adds support for reaction payload types in the omnibot message router. The key changes include:

• Adding a new reaction route test in router_test.py.
• Updating the message handling condition in router.py to route both 'message' and 'reaction' payload types.
• Expanding the routes dictionary and documentation to include the new 'reaction' match type.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
tests/unit/omnibot_receiver/router_test.py	Introduces a test case to validate reaction payload type routing.
omnibot_receiver/router.py	Updates the event handling condition and routes configuration to support reactions.