[UI] CSV Import modal: Add "Choose file" button functionality

[danoswaltCL]

User Story
As an experimenter, I can choose a CSV file from my computer to upload via the UI

(🟠 link to figma prototype)

Dependencies
#958
#964
#965

Links
Figma Screen Recording:
https://carnegielearning.slack.com/files/U02DS8JDP0Q/F05NH1DS0EP/screen_recording_2023-08-18_at_1.28.54_pm.mov

Acceptance Criteria
GIVEN a user clicks the "choose file" button
AND a pop-up opens with "choose file" button
THEN I will see an OS dialog to pick one csv file

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[🟠 does validation need to happen in UI or after submitting?]
GIVEN a user has selected and confirmed a file in the OS dialog
THEN the csv should be validated [🟠 include validation criteria here]

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[🟠 does validation need to happen in UI or after submitting?]
GIVEN that the csv is valid
THEN the UI should display [ 🟠 insert the text for a confirmation message ]
AND the button to import should be enabled

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[🟠 does validation need to happen in UI or after submitting?]
GIVEN that the csv is invalid
THEN the UI should display [ 🟠 some helpful text about why it is invalid ]
AND the button to import should remain disabled

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[zackcl]

QA: Passed