Make hledger-run-command more flexible

[shivjm]

Something I keep wishing for is a way to edit the command line that hledger-run-command runs. It would be useful if one could call it with a prefix argument to see and edit the final command before it was run, similarly to what M-x grep presents.

One alternative I can think of is to build a transient-based interface for hledger commands. This would probably be even more helpful, but also a big undertaking.