Add support for secret visibility types

[apazzolini]

This PR adds CLI support for secret visibility types. It:

• Correctly handles NULLs and includes the vistypes when using doppler secrets --json
• Prints [RESTRICTED] in the table when appropriate
• Adds the --visibility flag to explicitly show the visibility types in the table

Note that this should only be merged after visibility types has been released as the code expects the new properties from the API.

» doppler secrets
┌──────────────────────┬─────────────────────────────────────┬──────┐
│ NAME                 │ VALUE                               │ NOTE │
├──────────────────────┼─────────────────────────────────────┼──────┤
│ S1                   │ [RESTRICTED]                        │      │
│ S2                   │ v2                                  │      │
│ S3                   │ v3                                  │      │
└──────────────────────┴─────────────────────────────────────┴──────┘

» doppler secrets --visibility
┌──────────────────────┬────────────┬─────────────────────────────────────┬──────┐
│ NAME                 │ VISIBILITY │ VALUE                               │ NOTE │
├──────────────────────┼────────────┼─────────────────────────────────────┼──────┤
│ S1                   │ restricted │ [RESTRICTED]                        │      │
│ S2                   │ masked     │ v2                                  │      │
│ S3                   │ masked     │ v3                                  │      │
└──────────────────────┴────────────┴─────────────────────────────────────┴──────┘

» doppler secrets --visibility --raw
┌──────────────────────┬────────────┬──────────────┬────────────────┬──────────────────────────┬──────┐
│ NAME                 │ VISIBILITY │ VALUE        │ RAW VISIBILITY │ RAW VALUE                │ NOTE │
├──────────────────────┼────────────┼──────────────┼────────────────┼──────────────────────────┼──────┤
│ S1                   │ restricted │ [RESTRICTED] │ unmasked       │ ${stg.RESTRICTED_SECRET} │      │
│ S2                   │ masked     │ v2           │ masked         │ v2                       │      │
│ S3                   │ masked     │ v3           │ masked         │ v3                       │      │
└──────────────────────┴────────────┴──────────────┴────────────────┴──────────────────────────┴──────┘

» doppler secrets --json --raw | jq
{
  "S1": {
    "computed": null,
    "computedVisibility": "restricted",
    "note": "",
    "raw": "${stg.RESTRICTED_SECRET}",
    "rawVisibility": "unmasked"
  },
  "S2": {
    "computed": "v2",
    "computedVisibility": "masked",
    "note": "",
    "raw": "v2",
    "rawVisibility": "masked"
  },
  "S3": {
    "computed": "v3",
    "computedVisibility": "masked",
    "note": "",
    "raw": "v3",
    "rawVisibility": "masked"
  }
}

Closes ENG-6140