feat: support adding expenses

[dustinwhisman]

Description

This allows users to add expenses. The inputs have attributes to help with filling out the form, including for validation, autocapitalization, and input modes. They also accept default values, which will help for editing expenses later. There are a few helper methods for formatting input values, but everything is kept pretty basic. Will want to come back to this to add tests later.

To Validate

1. Make sure all PR Checks have passed
2. Pull down this branch
3. Run npm run dev and check for any unexpected changes
4. Click the "Add Expense" link on the overview page, confirming it loads a form with today's date pre-populated
5. Add an entry and submit the form, confirming it redirects you to the overview page with your new expense shown as expected

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