fix: misc integration-related fixes and improvements

[nunogois]

https://linear.app/unleash/issue/2-1401/misc-fixes-and-improvements-related-to-the-new-slack-app-integration

This includes multiple UI-related misc fixes and improvements that are not only related with the new Slack App integration but also integrations in general.

• Improves the styling in the "how does it work" section;
• Improves the text in the IntegrationMultiSelectors;
• Switches "Configure" and "Open" around to match designs;
• Properly handles click event on IntegrationCardMenu (fix navigation on dialog click);
• Fixes titles and contents for "enable/disable" and "delete" integration dialogs to match designs;
• Updates Slack App integration "how does it work" section to better reflect the intended behavior;
• Removes redundant alerts after previous point;
• Adds an alert in the old Slack integration configuration warning of its deprecation and suggesting the new Slack App integration instead;
• Fixes typos;
• Slight refactors;

Co-authored by @nicolaesocaciu

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[nicolaesocaciu]

LGTM!