Add team.externalTeams.list API support

[seratch]

This pull request adds team.externalTeams.list API to this SDK: https://api.slack.com/methods/team.externalTeams.list

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

Attention: Patch coverage is 73.33333% with 4 lines in your changes missing coverage. Please review.

Project coverage is 75.03%. Comparing base (56f2d26) to head (a889e7f).

Files	Patch %	Lines
...java/com/slack/api/methods/RequestFormBuilder.java	60.00%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #1327   +/-   ##
=========================================
  Coverage     75.02%   75.03%           
- Complexity     4172     4178    +6     
=========================================
  Files           446      446           
  Lines         12887    12902   +15     
  Branches       1329     1331    +2     
=========================================
+ Hits           9669     9681   +12     
- Misses         2443     2444    +1     
- Partials        775      777    +2     

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