Added S3 user management

[UtkarshBhatthere]

Added CLI to Create, Delete, List and Get S3 users for rgw

ubuntu@microcephtest:~$ sudo microceph s3 list
+---+-------------+
| # |    NAME     |
+---+-------------+
| 1 | test4       |
+---+-------------+
| 2 | testUser100 |
+---+-------------+
| 3 | test        |
+---+-------------+
| 4 | test2       |
+---+-------------+
| 5 | test5       |
+---+-------------+
ubuntu@microcephtest:~$ sudo microceph s3 get testUser100
+-------------+----------------------+------------------------------------------+
|    NAME     |      ACCESS KEY      |                  SECRET                  |
+-------------+----------------------+------------------------------------------+
| testUser100 | 9YI4KEEEZ333ES6Z5PST | iNPJDugy2l1GlnA8TWCWNguncQcb0f6glIjaj1Wu |
+-------------+----------------------+------------------------------------------+
ubuntu@microcephtest:~$ sudo microceph s3 create utkarsh --access-key=yo --secret=doesitwork?
+---------+------------+-------------+
|  NAME   | ACCESS KEY |   SECRET    |
+---------+------------+-------------+
| utkarsh | yo         | doesitwork? |
+---------+------------+-------------+
ubuntu@microcephtest:~$ sudo microceph s3 delete utkarsh
ubuntu@microcephtest:~$ sudo microceph s3 list
+---+-------------+
| # |    NAME     |
+---+-------------+
| 1 | test4       |
+---+-------------+
| 2 | testUser100 |
+---+-------------+
| 3 | test        |
+---+-------------+
| 4 | test2       |
+---+-------------+
| 5 | test5       |
+---+-------------+

[UtkarshBhatthere]

Added implementation, will add tests for the same.

[UtkarshBhatthere]

The PR lacks test, will remove from drafts once I have added them.

[UtkarshBhatthere]

@sabaini I have modified the APIs to be using ""services/rgw/user"".

[UtkarshBhatthere]

Thanks for the detailed review @sabaini 🙏🏼 . I will implement your RESTy suggestions in and make the PR ready.