Suggestion: Use Github API to render markdown previews

With issues such as #914, #834, #833, #825, #820 and #286, the markdown preview is not the same as what we will see on github.

Currently, the markdown preview uses a third-party library, ngx-markdown. While ngx-markdown is a good markdown library for angular applications, it does not give the same output as Github flavored markdown.

Let's use the Github API in [https://docs.github.com/en/rest/reference/markdown#render-a-markdown-document](https://docs.github.com/en/rest/reference/markdown#render-a-markdown-document) to render the markdown as html in the preview. While there might be minor differences in styling, the html should be the same as what we will see if we click preview on github.

Start by tracing the current ngx-markdown preview flow in the Angular application and review GitHub's markdown-rendering API documentation. Replace the third-party preview path with the API response, while accounting for the styling differences noted in the issue. Done means the preview HTML matches GitHub's rendered output for the reported markdown cases.

Written by the indexing model from the issue text.