feat: add -c flag to run cmds after init

[CatsDeservePets]

• Fixes Focus a dir when opening lf #2308

This PR introduces a new flag to execute commands after the client has been initialised. This fixes some of the shortcomings the current -command flag has due to its commands running before lf's UI has been established.

Name and functionality are highly inspired by Vim:

 +command, -c command
			 Execute command after reading the first file.  Up to
			 10 instances allowed.  "+foo" and -c "foo" are
			 equivalent.

 --cmd command
			 Like -c, but execute command before processing any
			 vimrc.  Up to 10 instances of these can be used
			 independently from instances of -c.