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)
• 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

Please read the Contributing guidelines and Code of Conduct before creating this issue or pull request. By submitting, you agree to those rules.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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

Additional details and impacted files

@@             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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