Adding Markdown and Preview feature inside "Write Post" within Donut

## Problem to be solved

Currently, there is a button inside the donut platform on the dashboard page which on clicking redirects to write any post. But the actual sense of having the "Write post" comes with proper markdown and preview option. So the purpose of this I to develop the same mechanism and frontend as we see within the GitHub Issue and implement within the **Write Post**.
It should be implemented in the same way as an image depicts:

After it is done, please upload the screenshot for the same.