Add admin.apps.uninstall support

[seratch]

Summary

This pull request adds admin.apps.uninstall API support. The endpoint is available only for Enterprise Grid organizations.

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

• slack_sdk.web.WebClient (sync/async) (Web API client)
• slack_sdk.webhook.WebhookClient (sync/async) (Incoming Webhook, response_url sender)
• slack_sdk.models (UI component builders)
• slack_sdk.oauth (OAuth Flow Utilities)
• slack_sdk.socket_mode (Socket Mode client)
• slack_sdk.audit_logs (Audit Logs API client)
• slack_sdk.scim (SCIM API client)
• slack_sdk.rtm (RTM client)
• slack_sdk.signature (Request Signature Verifier)
• /docs-src (Documents, have you run ./docs.sh?)
• /docs-src-v2 (Documents, have you run ./docs-v2.sh?)
• /tutorial (PythOnBoardingBot tutorial)
• tests/integration_tests (Automated tests for this library)

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've run python setup.py validate after making the changes.

[codecov]

Codecov Report

Merging #1011 (1fa232b) into main (7d28505) will increase coverage by 0.00%.
The diff coverage is 88.88%.

@@           Coverage Diff           @@
##             main    #1011   +/-   ##
=======================================
  Coverage   86.58%   86.58%           
=======================================
  Files          95       95           
  Lines        8749     8776   +27     
=======================================
+ Hits         7575     7599   +24     
- Misses       1174     1177    +3     

Impacted Files	Coverage Δ
slack_sdk/web/async_client.py	94.42% <88.88%> (-0.07%)	⬇️
slack_sdk/web/client.py	95.91% <88.88%> (-0.09%)	⬇️
slack_sdk/web/legacy_client.py	95.78% <88.88%> (-0.09%)	⬇️

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