feat(run_template): allow overriding search params when running templates

[GustavoKatel]

A nice to have that I think more people might find useful

The reason behind it is that I often find myself opening files from outside of :cwd but still want to use the $PWD/Makefile

In my config I then have

	overseer.run_task({
		search_params = {
			dir = vim.fn.getcwd(),
			filetype = vim.bo.filetype,
		},
	}, function(task) 
        ....
        end)

[stevearc]

Sure, this seems like a reasonable extension. Thanks!