Flarum uses the TextFormatter library to format the post content. That library has a plugin (disabled by default) called "PipeTables" that implements that syntax https://s9etextformatter.readthedocs.io/Plugins/PipeTables/Syntax/
That TextFormatter plugin can be enabled using this Flarum extension and selecting the "PipeTables" option https://discuss.flarum.org/d/17770-friendsofflarum-formatting
There's currently no plan to enable that option by default in Flarum. Flarum's Markdown and BBcode extensions intentionally come without any setting for simplicity so I don't think we would want to add a switch for tables inside of the Markdown extension. I'm not sure if it's a common enough feature to justify enabling by default in Flarum.