Add Options / initial_options validation

[srajiang]

Suggestion raised in: #1509

Behavior:
initial_options options must contain an exact match of options provided, or users experience issues with properly updating forms. Suggestion has been raised to update this SDK to notify developers when an option provided does not exactly match an initial_options selection.

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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