28582: debug: add encryption-status command. r=mberhault a=mberhault

When encryption is enabled, this outputs full key details and associated
files.

Shows the hierarchy of store keys, data keys, and files.

We do not currently show encryption progress as it requires opening
rocksdb in read/write mode. This will eventually be added.

For example, this is the output on a store that has had two different
store keys and multiple data keys:

```
$ ./cockroach debug encryption-status --enterprise-encryption=path=cockroach-data,key=keys/aes-192.key,old-key=keys/aes-128.key cockroach-data
[
  {
    "ID": "222430e9b9e6bdb54b66dcb4124778da6c284a9d47e6a1637e0b26d059e61a80",
    "Type": "AES128_CTR",
    "Created": "2018-06-19 09:59:38 -0400 EDT",
    "Source": "/store/cockroach/src/github.com/cockroachdb/cockroach/keys/aes-128.key",
    "DataKeys": [
      {
        "ID": "1cfd71ab16fdc332aea838ae70b7952f28bfd247fd9da8ebef03d9576f8b7d30",
        "Created": "2018-06-19 09:59:38 -0400 EDT",
        "Files": [
          "IDENTITY"
        ]
      }
    ]
  },
  {
    "ID": "dc8a5767b73746f69c9245fe01688c0f9b934adb2b592d2d199c4a85f6d72d93",
    "Active": true,
    "Type": "AES192_CTR",
    "Created": "2018-06-19 14:04:04 -0400 EDT",
    "Source": "/store/cockroach/src/github.com/cockroachdb/cockroach/keys/aes-192.key",
    "Files": [
      "COCKROACHDB_DATA_KEYS"
    ],
    "DataKeys": [
      {
        "ID": "72b1a1162dbcc934f3d6c275ca845c1bfb74e81c24d9779132017ad5defcb7de",
        "Created": "2018-06-19 14:04:04 -0400 EDT"
      },
      {
        "ID": "99f26acfaf9004ebcfc8f7fad8d06e54ab101d5b3c77a0b7f912f5b270884564",
        "Created": "2018-07-09 11:59:11 -0400 EDT"
      },
      {
        "ID": "123df81c7ad822168bf2e84502691c68a07bba5af52e66b7b33751306c4ac9a8",
        "Active": true,
        "Created": "2018-08-08 07:16:27 -0400 EDT",
        "Files": [
          "000166.log",
          "000169.sst",
          "CURRENT",
          "MANIFEST-000165",
          "OPTIONS-000165",
          "OPTIONS-000168"
        ]
      }
    ]
  }
]
```

And on a store running with just plaintext (still with encryption flag
passed):
```
$ ./cockroach debug encryption-status --enterprise-encryption=path=cockroach-data2,key=plain,old-key=plain cockroach-data2
[
  {
    "ID": "plain",
    "Active": true,
    "Type": "Plaintext",
    "Created": "2018-06-19 14:24:31 -0400 EDT",
    "Source": "plain",
    "Files": [
      "000109.log",
      "000112.sst",
      "CURRENT",
      "MANIFEST-000108",
      "OPTIONS-000108",
      "OPTIONS-000111"
    ],
    "DataKeys": [
      {
        "ID": "plain",
        "Active": true,
        "Exposed": true,
        "Created": "2018-06-19 14:24:31 -0400 EDT"
      }
    ]
  }
]
```

A store that does not even use the file registry will not output
anything (eg: a store without the `--enterprise-encryption` flag).

Release note (enterprise change): add encryption-status debug command to
display encryption key information.

Co-authored-by: marc <marc@cockroachlabs.com>