Add Tags to the frontend (sidebar and form)

[Leila-U]

• Add textbox for tags at the bottom of the event form with a 50 letter limit
• Add a row for tags in the event list item

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit 7327a35):

https://utmap-c252d--pr114-issue-104-tags-front-bgxx1rg1.web.app

_{(expires Sun, 11 Apr 2021 22:37:58 GMT)}

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