Add bisect menu entry that lets you choose bisect terms

This can be useful if you want to find the commit that fixed a bug (you'd use
"broken/fixed" instead of "good/bad" in this case), or if you want to find the
commit that brought a big performance improvement (use "slow/fast"). It's pretty
mind-bending to have to use "good/bad" in these cases, and swap their meanings
in your head.

Thankfully, lazygit already had support for using custom terms during the bisect
(for the case that a bisect was started on the command-line, I suppose), so all
that's needed is adding a way to specify them in lazygit.

pkg/commands/git_commands/bisect.go

@@ -121,6 +121,15 @@ func (self *BisectCommands) Start() error {
 	return self.cmd.New(cmdArgs).StreamOutput().Run()
 }
 
+func (self *BisectCommands) StartWithTerms(oldTerm string, newTerm string) error {
+	cmdArgs := NewGitCmd("bisect").Arg("start").
+		Arg("--term-old=" + oldTerm).
+		Arg("--term-new=" + newTerm).
+		ToArgv()
+
+	return self.cmd.New(cmdArgs).StreamOutput().Run()
+}
+
 // tells us whether we've found our problem commit(s). We return a string slice of
 // commit sha's if we're done, and that slice may have more that one item if
 // skipped commits are involved.