feature: Add a demo example for PyCon APAC 2023 talk

[achimnol]

This is a new example script to demonstrate various features of aiomonitor, including preserving termination logs for long-running tasks and exposing several start_monitor() options as CLI arguments.

$ python ./examples/demo.py --help

Note

Having a large number of timers and a short history limit may remove the termination traces too early.

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> (e.g. 588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the PR
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: Fix issue with non-ascii contents in doctest text files.