Custom Journey Creation Frontend

[ambers7]

Summary

This pull request is the first step towards implementing the Custom Journey Creation Frontend. The Custom Journey page has the fields Journey Name, Categories, Difficulty Level, Start Date, Description. Creates an EventBase with the filled in fields and passes that onto the next page.

• only one of each Category and Difficulty Level selection pills can only be selected
• Next button is disabled until all fields are filled, as shown by a displaytoast
• DateTime picker uses the flutter_datetime_picker_plus package (https://fluttergems.dev/packages/flutter_datetime_picker_plus/), and shows up once the box under "Start Date" is tapped

Remaining TODOs:

• ensure past dates/times are invalid during creation
• ensure text box inputs are valid
• replace placeholder challenge creation page with the real one
• find a place for the 100 points to go, since currently journeys don't have points in the backend, only challenges (design)
• move to the "Create" section of the bottom bar once that is implemented

Notes: affects the onboarding screens shown

Test Plan

• Test on different simulators
• Test trying to create a journey with not all of the fields filled out or invalid fields filled out

[dti-github-bot]

[diff-counting] Significant lines: 3643. This diff might be too big! Developer leads are invited to review the code.

[jiminkim214]

Great job Amber! One thing to consider is adding a bit more documentation/comments as you build. Overall, looking solid!