Added --validate flag to twitch token

[Xemdo]

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Problem/Feature

Solved #271 by adding --validate to twitch token

Description of Changes:

Added --validate flag to twitch token:

$ ./twitch-cli token --validate <user token>
Client ID: 718ozxefxg7qak0jsvmrahw9pq3qch
Token Type: User Access Token
User ID: 57047445
User Login: xemdo
Expires In: 15145 (Sat, 23 Sep 2023 06:15:33 UTC)
Scopes:
- channel:read:polls
- channel:read:vips
- user:read:follows
- user:read:subscriptions

$ ./twitch-cli token --validate <app token>
Client ID: dy5l2nnrf1fybxoupqb73kw5ksqhw6
Token Type: App Access Token
Expires In: 5053085 (Mon, 20 Nov 2023 13:41:43 UTC)
Scopes: None

Checklist

• [X] My code follows the Contribution Guide
• [X] I have self-reviewed the changes being requested
• [X] I have made comments on pieces of code that may be difficult to understand for other editors
• [X] I have updated the documentation (if applicable)