Adding support for the following methods to WebClient:

• https://api.slack.com/methods/admin.barriers.create
• https://api.slack.com/methods/admin.barriers.delete
• https://api.slack.com/methods/admin.barriers.list
• https://api.slack.com/methods/admin.barriers.update

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

• slack_sdk.web.WebClient (Web API client)
• slack_sdk.webhook.WebhookClient (Incoming Webhook, response_url sender)
• slack_sdk.models (UI component builders)
• slack_sdk.oauth (OAuth Flow Utilities)
• slack_sdk.rtm.RTMClient (RTM client)
• slack_sdk.signature (Request Signature Verifier)

Requirements

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