code monitors: add create/update for slack actions

Created by: limitedmage

Part of #27163 (closed)

• Adds CRUD for Slack webhook actions.
• Adds detailed unit tests for ActionEditor, EmailAction and SlackWebhookAction. This required a bit of refactoring around test IDs and the test email GraphQL call. Integration tests were also updated to use the new test IDs.
• Adds storybook tests for EmailAction and SlackWebhookAction.
• Removes experimentalFeature.showCodeMonitoringTestEmailButton since it no longer applies with the new design. CodeMonitorNode.test.tsx was removed since this was the only thing that file tested.
• Some props in the code monitoring code were renamed for better readability.
• Slack webhooks were added to mock data for code monitor tests.

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