[Onboarding] - #2786 created model for checklist

[Aaryan1203]

Changes

Created the model for checklist
Created the frontend type for checklist
Added faq and milestones to the shared file to import them more easily

Note

• A checklist has a name, description, a list of subtasks, and a teamtype.
• The name represents the name of the checklist (ex. Join Slack)
• The list of subtasks is a string because they will represent the individual tasks (ex. put your name and pronouns).
• The description will be for the grey block on the side.
• The team type is because each checklist will be assocaited with a team type. If there is no team type, it is a part of the general checklist, otherwise it is a part of the specified team types checklists

Closes #2786