Issue 103 tags backend data schema

[RiddleMeDoo]

• Added tags to the database schema
• Updated Event object to include tags
• If events do not have tags in the database return an empty list to client
• Updated documentation to include tags

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit 3dc4bee):

https://utmap-c252d--pr110-issue-103-tags-backe-dhqs00en.web.app

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