Enable using RetryHandler for 200 OK response patterns

[seratch]

Currently, the retry handler mechansim is not available for the patterns with a 200 OK response from Slack. However, in some cases, developers may need to do retries such as "fatal_error" error code responses.

This feature enhancement is specifically needed for WebClient and AsyncWebClient. Slack's Web APIs can return a 200 OK response even when the response is an error.

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)

Requirements

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