Markdown doc refactor - squashed

Change emoji to Gitlab rendering and fix typo

Use built in renderer for math

Touchups to GFM Doc and bring in suggestions from MR 22122

Fix link

Add epics to align docs

Add epic badge

Fix dashes making accidental headers, and move wikis down, add emoji note

Add section explaining GitLab markdown extensions

Update to incorporate recent changes

Add links rendering, fix issue rendering as color chip

Add links rendering, fix issue rendering as color chip

Update links to GitLab rendered version of markdown doc

Separate GFM extensions, reorder list, other tweaks

Update code blocks and highlighting

Trying to fix improper markdown rendering

Fix rendering broken by triple backticks and add emoji note

testing triple tildes instead of quad backticks

testing rending after mermaid

Various fixes to improve markdown rendering

Update markdown doc after review

Fix markdown doc after review, part two

fix typo in markdown doc

doc/user/project/settings/index.md

@@ -18,7 +18,7 @@ Adjust your project's name, description, avatar, [default branch](../repository/
 
 ![general project settings](img/general_settings.png)
 
-The project description also partially supports [standard markdown](../../markdown.md#standard-markdown). You can use [emphasis](../../markdown.md#emphasis), [links](../../markdown.md#links), and [line-breaks](../../markdown.md#line-breaks) to add more context to the project description.
+The project description also partially supports [standard markdown](../../markdown.md#standard-markdown-and-extensions-in-gitlab). You can use [emphasis](../../markdown.md#emphasis), [links](../../markdown.md#links), and [line-breaks](../../markdown.md#line-breaks) to add more context to the project description.
 
 ### Sharing and permissions