Implement List Beta Groups

[adamjcampbell]

Implements the list beta groups command Closes #99

📝 Summary of Changes

Changes proposed in this pull request:

• Makes app required for a betaGroup
• Changes BetaGroup creationDate to an ISO8601 formatted data string
• Adds ListBetaGroupsOperation as well as associated commands and options
• Starts moving to a pattern where we can throwing functions on the service and can then leverage multiple operations

⚠️ Items of Note

Now that we have a nested App model under BetaGroup we aren't showing all values as they would be decoded in json or yaml. Do we want to show every data field in the table? It's getting pretty long.

🧐🗒 Reviewer Notes

💁 Example

USAGE: asc testflight betagroup list [--api-issuer <uuid>] [--api-key-id <keyid>] [--csv] [--json] [--table] [--yaml] [--filter-app-ids <filter-app-ids> ...] [--filter-bundle-ids <filter-bundle-ids> ...]

🔨 How To Test

>  swift run asc betagroup list
+------------+------------------+----------+-----------------+-------------+-------------+---------------------+-------------------+---------------------------+----------------------+
| App ID     | App Bundle ID    | App Name | Group Name      | Is Internal | Public Link | Public Link Enabled | Public Link Limit | Public Link Limit Enabled | Creation Date        |
+------------+------------------+----------+-----------------+-------------+-------------+---------------------+-------------------+---------------------------+----------------------+
| 1234567890 | com.example.test | Test App | Example Group 1 | true        |             |                     |                   |                           | 2020-04-08T07:40:14Z |
+------------+------------------+----------+-----------------+-------------+-------------+---------------------+-------------------+---------------------------+----------------------+