#2223: Design Review mark user confirmation endpoint

[martin0he]

Changes

created an endpoint that marks the current user as confirmed for a given design review, and sets their schedule setting's availability to the given availability array

Test Cases

• When the user doesn't have schedule settings
• When the array of availabilities has only 1 element
• given user isn't optional nor required
• availabilities arent between 0 and 83 inclusive
• when the design review doesn't exist
• when the design review has been deleted

Screenshots

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Closes #2223

[martin0he]

this is my postman setup

[RChandler234]

LGTM 🔥