Add Hashtag Generation functionality to doc2pen

[phreakyphoenix]

I propose to add a new page to the site, which will enable a user to upload any public image URL and obtain n relevant hashtags for the same.

The front end will include a functional UI, with two text boxes, one for the URL and one for the number of hashtags the user wants (n).

The backend will be in React in keeping with the rest of the site and use an API to get AI-generated hashtags for the uploaded image.