Include release dates in registry listings

## Description

Currently the listings for each plug-in include no information on when a plug-in was released.

## Possible Solution

Consider adding a _“last modified”_ date to the listing page to show when the plug-in JSON file in the repo was last updated.

This info could be based on the commit date or the date the PR was merged:

> Last modified Feb 16, 2024

## Potential Alternatives

For plug-ins with multiple versions, it might be better to extract the date from the release tag for each version, and display it next to the version numbers in the **Versions** section:

> ### Versions
> - [3.1.0](https://www.dita-ot.org/plugins/net.infotexture.dita-bootstrap/3.1.0) released Nov 1, 2018
> - [3.2.0](https://www.dita-ot.org/plugins/net.infotexture.dita-bootstrap/3.2.0) released Sep 19, 2021

Start by inspecting how the registry listing pages and plug-in version data are generated. Clarify whether the project should show a single last-modified date or release dates for each version; done means the chosen dates appear correctly in the relevant listing pages.

Written by the indexing model from the issue text.