Add CurrentUser#recently_viewed_issues field to GraphQL API

What does this MR do and why?

This merge request adds a new feature to display recently viewed issues for the current user in GitLab's GraphQL API. It introduces a new resolver called RecentIssuesResolver, which fetches the most recently viewed issues for the authenticated user. The feature is added to the CurrentUserType in the GraphQL schema, allowing clients to query for recently viewed issues. The changes also include documentation updates and a new test file to ensure the functionality works as expected. This feature is marked as experimental and is set to be introduced in GitLab version 17.9.

This MR is a step towards building a prototype of a personalized GitLab homepage.

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• Closes Surface recently viewed issues in GraphQL API (#514805 - closed)

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