Add list objects api

[cesnietor]

For #290
This includes the basic information of an object.
This api can be called using /api/v1/buckets/{bucket_name}/objects?prefix={prefix}&recursive={true|false}
Where prefix is a folder and recursive is used to traverse across the folders.

e.g. GET on /api/v1/buckets/bucket1/objects?recursive=false:
Response Payload:

{
    "objects": [
        {
            "last_modified": "2020-09-28 23:21:02.235 +0000 UTC",
            "name": "file.csv",
            "size": 45813
        },
        {
            "last_modified": "2020-09-28 23:22:08.562 +0000 UTC",
            "name": "photo.jpg",
            "size": 103614
        },
        {
            "last_modified": "0001-01-01 00:00:00 +0000 UTC",
            "name": "inky/"
        }
    ],
    "total": 3
}

With prefix parameter:
/api/v1/buckets/bucket1/objects?prefix=inky/&recursive=false

{
    "objects": [
        {
            "last_modified": "2020-09-28 23:25:31.171 +0000 UTC",
            "name": "inky/.gitignore",
            "size": 330
        },
        {
            "last_modified": "2020-09-28 23:25:31.17 +0000 UTC",
            "name": "inky/.stickler.yml",
            "size": 72
        },
        {
            "last_modified": "0001-01-01 00:00:00 +0000 UTC",
            "name": "inky/.git/"
        },
        {
            "last_modified": "0001-01-01 00:00:00 +0000 UTC",
            "name": "inky/examples/"
        },
        {
            "last_modified": "0001-01-01 00:00:00 +0000 UTC",
            "name": "inky/library/"
        },
    ],
    "total": 5
}

• Tests included

[bexsoft]

LGTM