Can we have a no-ff (non-fast forward) merge? Revisit #785

[doublethefish]

Is your feature request related to a problem? Please describe.
Depending on which project I am contributing to, I often switch between using --no-ff or not. Often it is older projects that prefer --no-ff merge strategies. An inbuilt --no-ff optional merge type in lazygit is needed, in addition to the config and custom commands.

Describe the solution you'd like
It would be incredibly useful to have a default merge type that adheres to the config as per solution to #785, AND an explicit --no-ff.

Describe alternatives you've considered

1. global config ~/.config/.*/config.yml
   • switching between projects that require --no-ff requires that I drop to terminal
   • or configure each repo separately (see below)
   • requires that global config is sync'd between system (which I have so maybe not an issue for me)
2. silent per repo config <repo>/.git/lazygit.yml
   • If I were to add <repo>/.git/lazygit.yml to each repo I need to ensure that on each checkout of that repo, on each machine, that I have the config.
3. committed per repo config <repo>/**/.lazygit.yml
   • requires committing to each repo (overhead)
   • pollutes each repo
   • is reliant on maintainers being ok with committed config for tools they may not use/support
4. custom commands
   • similar to 1 and 2 above

Additional context
--no-ff is such a typical, and useful, workflow but is no longer the standard so having a one-size-fits all solution in this case doesn't work. Two merge types are needed.

However in the keyboard-wizard world of lazygit I'm not quite sure how this would be best implmented.