Incorrect mime type for .css files after uploading docs to S3

[nirinchev]

Discussed briefly in this slack thread: https://mongodb.slack.com/archives/CLY6HQWUE/p1707132051820689

tl;dr: looks like our upload to S3 pushes the .css files as text/plain and we need to add the --guess-mime-type argument to the s3cmd calls here:

realm-swift/build.sh

Lines 1087 to 1091 in dfb165e

	s3cmd put --recursive --acl-public --access_key=${AWS_ACCESS_KEY_ID} --secret_key=${AWS_SECRET_ACCESS_KEY} swift_output/ s3://realm-sdks/docs/realm-sdks/swift/${VERSION}/
	s3cmd put --recursive --acl-public --access_key=${AWS_ACCESS_KEY_ID} --secret_key=${AWS_SECRET_ACCESS_KEY} swift_output/ s3://realm-sdks/docs/realm-sdks/swift/latest/
	s3cmd put --recursive --acl-public --access_key=${AWS_ACCESS_KEY_ID} --secret_key=${AWS_SECRET_ACCESS_KEY} objc_output/ s3://realm-sdks/docs/realm-sdks/objc/${VERSION}/
	s3cmd put --recursive --acl-public --access_key=${AWS_ACCESS_KEY_ID} --secret_key=${AWS_SECRET_ACCESS_KEY} objc_output/ s3://realm-sdks/docs/realm-sdks/objc/latest/