feat: rename 'Description' to 'Overview' in MR items

Kevrequested to merge
KevSlashNull/gitlab-vscode-extension:rename-description-to-overview into main

This MR renames Description to Overview in the MR items in the “Issues and Merge Requests” sidebar section. The reason is that the GitLab UI calls the show page of merge requests “Overview” (see the image below). The term Description is also not accurate (anymore?) because the webview page displays meta information, the description, and comments.

Screenshots

Before After Reference
the item is called Description the item is called Overview the GitLab UI calls the page Overview too

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