Add "No Merges" Option to Git Graph to Hide Merge Commits

[sahilpatani-ts]

Enhance the Git Graph view by adding a "No Merges" option that allows users to hide merge commits. This feature can be implemented as:

• A checkbox within the Git Graph UI labeled "No Merges" to toggle the visibility of merge commits.
• A configuration setting (e.g., gitGraph.noMerges) in the extension settings for users who prefer a persistent option.

Expected Behavior:

When the "No Merges" option is enabled, the Git Graph should exclude all merge commits, providing a cleaner and more linear view of the commit history.