feat: no-merges

[real420og]

PR Description

Repositories with frequent merges – merge commits take up a significant part of the history.

Enhancing the filter with --no-merges provides a clean history of changes.

lazygit_no_merges_2.mov

Please check if the PR fulfills these requirements

• Cheatsheets are up-to-date (run go generate ./...)
• Code has been formatted (see here)
• Tests have been added/updated (see here for the integration test guide)
• Text is internationalised (see here)
• If a new UserConfig entry was added, make sure it can be hot-reloaded (see here)
• Docs have been updated if necessary
• You've read through your own file changes for silly mistakes etc