Add team.externalTeams.disconnect API

[seratch]

This pull request adds a new API endpoint to slack-api-client library: https://api.slack.com/methods/team.externalTeams.disconnect

Category (place an x in each of the [ ])

• [ ] bolt (Bolt for Java)
• [ ] bolt-{sub modules} (Bolt for Java - optional modules)
• [x] slack-api-client (Slack API Clients)
• [ ] slack-api-model (Slack API Data Models)
• [ ] *slack-api--kotlin-extension** (Kotlin Extensions for Slack API Clients)
• [ ] slack-app-backend (The primitive layer of Bolt for Java)

Requirements

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 75.06%. Comparing base (2ae1fa3) to head (f3961f4).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1331 +/- ## ============================================ + Coverage 74.93% 75.06% +0.13% - Complexity 4176 4188 +12 ============================================ Files 446 446 Lines 12912 12920 +8 Branches 1331 1331 ============================================ + Hits 9675 9699 +24 + Misses 2461 2448 -13 + Partials 776 773 -3 ```

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