Add micro (pre-)release dates to JSON and as tables

[CAM-Gerlach]

Followup to #998 (which would be implemented first, since it is more important and lower-hanging fruit).

As [discussed] on PR #988 and at the Python Docs Community meeting, it would be helpful to the release date of each micro release/pre-elease to the Status of Python versions JSON and page. This would be useful as both exposing this information, currently manually listed in each release PEP, in a machine-readable form, as well as generating standard, easily skimmable human-readable tables linked from the main version table and all on one page.

If this works out, we could then have the release PEPs just link the appropriate section on this page, or automatically inject the table via the same csv-table directive as used here, avoiding the need for RMs/others to update multiple places

Someone even suggesting adding a small dot to the chart for each version release, though we'd have to see if it makes it too cluttered.