US #2 - (frontend) Update draft post UI to include a checkbox handling the post's anonymous state

[ericlin2]

Estimated effort: Medium/High
Dependencies among tasks: #12
Acceptance Criteria: When drafting a post, there is a checkbox that users can check to make the post anonymous. Upon creating the post, the post's anonymous state becomes true. If the checkbox is not checked when creating a post, the anonymous state is false.