add ability to run `lazygit origin/other-branch`

[teto]

Is your feature request related to a problem? Please describe.
A feature I like in tig is that I can quickly check other branches with tig origin/other-branch. I would like to start lazygit similarly with lazygit origin/other-branch and have it use the specific branch.

[jesseduffield]

Would you want it to open with that branch selected in the branches panel, and with the branches panel maximised? That sounds simple enough to me. Although I would use an arg like lazygit -b origin/other-branch

[teto]

I would like to see the commits of that branch. But I didn't know you could maximize the branch-panel, how do you do that ? it might be more interesting, I need to try first.
I think it's ok to have a flag if you want to reserve posiitional args for future usage.

[jesseduffield]

In pkg/gui/gui.go we use a half screen for when you pass the -f flag for filtering commits based on file:

	initialContext := contexts.Files
	if filterPath != "" {
		screenMode = SCREEN_HALF
		initialContext = contexts.BranchCommits
	}

Within the app you can also maximise a window with + and -

[teto]

ho cool indeed ! I tmay make sense to maximize the window or at least put it half screen. If there is a flag to control this, then it's not necessary.
I am a very basic user of lazygit, I use it mostly to git add (-p) files when I think it will be faster than the terminal's. I prefer to use tig to navigate at commits, out of habits so that's not an informed decision :)

[jesseduffield]

Yeah tig is better with viewing commits at the moment, but soon enough we will overtake it and achieve world domination!