Add channel shared events

[ldub]

added shared/unshared events

[Copilot]

Pull Request Overview

This PR adds support for Slack channel shared and unshared webhook events to the Haskell Slack API library. The implementation includes parsing JSON webhook payloads for these events and converting them to appropriate Haskell data types.

• Added data types ChannelSharedEvent and ChannelUnsharedEvent with appropriate fields
• Implemented JSON parsing for both event types in the Event sum type
• Added comprehensive test coverage with golden test files

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/Web/Slack/Experimental/Events/Types.hs	Added new data types and JSON parsing for channel shared/unshared events
tests/Web/Slack/Experimental/Events/TypesSpec.hs	Added test cases for the new event types
tests/golden/SlackWebhookEvent/channel_shared.json	Test data for channel shared event
tests/golden/SlackWebhookEvent/channel_shared.golden	Expected parsing output for channel shared event
tests/golden/SlackWebhookEvent/channel_unshared.json	Test data for channel unshared event
tests/golden/SlackWebhookEvent/channel_unshared.golden	Expected parsing output for channel unshared event

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