feat: enable loading videos from s3

[suryatejreddy]

This PR adds support for loading video datasets from S3.

Sample Queries

• LOAD VIDEO 's3://bucket/dummy.avi' INTO MyVideo;
• LOAD VIDEO 's3://bucket/eva_videos/*.mp4 INTO MyVideos;

Design Decisions

• The video files are downloaded to a directory s3_download_dir inside the config and by default points to inside the .eva folder.
• This would add redundancy but will be removed in a future PR that removes data duplicity by adding symlinks.

Testing

• Added test cases for single and multi-video loading

[gaurav274]

If we don't download s3 files, will it result in a significant logic change? How do other projects handle this?

[gaurav274]

Add changes to the https://github.com/georgia-tech-db/eva/blob/master/CHANGELOG.md

[xzdandy]

If we don't download s3 files, will it result in a significant logic change? How do other projects handle this?

We can store the "path" to s3 files with prefix (e.g., s3://..., local://....), and have different GET executors. The optimizer will choose the correct executor.