Use markdown table instead of HTML in docker_images_list

[dbkinder]

This document unnecessarily uses HTML for tables where markdown syntax would work just fine. It's also using styles on table elements that aren't supported, e.g., .class="tg-cly1". As written, this doesn't render well when published to the OPEA documentation HTML website.

For example this embedded HTML in the markdown file:

  <tr>
    <td class="tg-yk8o"><a href="https://hub.docker.com/r/opea/chatqna-ui">opea/chatqna-ui</a></td>
    <td class="tg-yk8o"><a href="https://github.com/opea-project/GenAIExamples/blob/main/ChatQnA/docker/ui/docker/Dockerfile">Link</a></td>
    <td class="tg-cly1">The docker image acted as the chatqna UI entry for facilitating interaction with users for question answering</td>
  </tr>

should be simplified into this so it renders well on both github.com and the published doc website:

| [open/chatqna-ui](https://hub.docker.com/r/opea/chatqna-ui) | [Dockerfile](https://github.com/opea-project/GenAIExamples/blob/main/ChatQnA/docker/ui/docker/Dockerfile) | The docker image acted as the chatqna UI entry for facilitating interaction with users for question answering |