fix: ResourceGroups lastUpdated time format

[dmurray-lacework]

Summary

The resourceGroups last updated type is now of type lacework.Epoch.
The cli table output for resource group show <id> lastUpdated is now RFC3339
The cli output for resource group show <id> --json & resource group list --json now shows lastUpdated as RFC3339

How did you test this change?

Manually run:
resource group show <id>
resource group show <id> --json
resource group list --json

Issue

https://lacework.atlassian.net/browse/ALLY-659

Usage:

Before

❯ lacework rg show <ID> --json
{
  "resource_group": {
  ...
      ],
      "lastUpdated": 1635519644365,
      "updatedBy": "[email protected]"
    }


❯ lacework rg show <ID>
                        RESOURCE ID                          TYPE               NAME                STATE    DEFAULT  
-----------------------------------------------------------+------+------------------------------+---------+----------
...
                RESOURCE GROUP PROPS                
----------------------------------------------------
    DESCRIPTION                                     
    UPDATED BY     [email protected]    
    LAST UPDATED   1635519644365                    
    ACCOUNT IDS    *         

After

❯ lacework rg show <ID> --json
{
  "resource_group": {
  ...
      ],
      "lastUpdated": "2021-10-29T15:00:44Z",
      "updatedBy": "[email protected]"
    },


❯ lacework rg show <ID>       
                        RESOURCE ID                          TYPE               NAME                STATE    DEFAULT  
-----------------------------------------------------------+------+------------------------------+---------+----------
  ...
                RESOURCE GROUP PROPS                
----------------------------------------------------
    DESCRIPTION                                     
    UPDATED BY     [email protected]    
    LAST UPDATED   2021-10-29T15:00:44Z             
    ACCOUNT IDS    *    

[afiune]

A few comments but the code looks good and runs pretty nice!