Add S3 contents functionalities

[DenisaCG]

Use the AWS SDK to get and manipulate the contents of S3 buckets.

Functionalities added:

• automatically connect to an S3 client using user credentials stored locally (they are extracted for those using the AWS CLI)
• set the CORS rules for a bucket needed to make the operations work
• list contents of a bucket, of a folder/sub-folder or retrieve contents of a file - the get function
• create a new file or directory (including the logic to increment untitled file names)
• delete a file or directory (including all of the files inside the directory)
• rename a file or directory (along with the logic to automatically rename all paths for the files inside renamed directory)
• logic to increment file names, such that the user doesn't accidentally overwrite files in case of renaming a file an existing file name
• edit and save a file
• copy a file or a directory to a new location within the bucket
• upload a new file and its contents from local storage to the bucket
• new toolbar button which allows user to switch to a new bucket
• new toolbar button which allows user to create a new bucket (work in progress - although button exists, we might not have the possibility to set the CORS rules necessary to create a bucket)
• support for all JLab file types (.txt, .ipynb, .csv, .pdf, .png, etc).

The current PR should add all functionalities needed such that the S3 bucket can be used as a file system in JupyterLab.

screenrecording-jupyter-drives-browser-demo.webm