docs: make a small set of examples for logger best practices

[dshemetov]

Ah I didn't know that! Do we have a space/documentation/reference for best practices like these?

Originally posted by @aysim319 in #2025 (comment)

I'm thinking we can just show a couple templates and a couple of the features of structlog.

[melange396]

There are many existing instances of good logging in our repositories that you could choose from for this. However, i don't think examples alone will be able to fully demonstrate all of the necessary principles;

The following comment (modified from the initial description of #2025) is worth adding before the simple logger examples in

covidcast-indicators/_delphi_utils_python/README.md

Line 23 in d52dcd5

## Logger Usage

and in the top docstring of the logger module itself¹:

"""

To make our structured logging as useful as it can be, particularly within the context of how we use logs in Elastic, the event argument (typically the first unnamed arg) should be a static string (to make filtering easier), and each dynamic/varying value should be specified in an individual meaningfully- and consistently-named argument to the logger call (for use in filtering, thresholding, grouping, visualization, etc).

"""

Footnotes

1. while editing that docstring we should also remove these now-outdated instructions: https://github.com/cmu-delphi/covidcast-indicators/blob/d52dcd5a6b84083fb5cbca4164ebdd8429ac81d3/_delphi_utils_python/delphi_utils/logger.py#L5-L8 ↩