feat(backend): prevent client arbitrary video status in request body

[keanu-a]

Summary

processStatusUpdate originally allowed the client to send an arbitrary video status in request body. Changed it to accept only UPLOADED if the video exist in S3 to prevent an authenticated user from spamming /PATCH to a resource that doesn't exist and will trigger more Mux calls. This will prevent any unnecessary calls to Mux that can increase spending.

Changes

• Created an AWS credentials bean since S3Client is its own bean now and shares credentials with the S3Presigner.
• Made sure object exists in S3 before calling Mux
• Made sure client only sends UPLOADED before calling mux

Tests

• Tested end-to-end on postman: initiate upload -> send to s3 -> process update
• Tested new requests errors like contentType in CreateVideoRequest, videoStatus follows enum