Support `cond` command

[gozes]

I tend to use the cond command a lot when debugging tests just to get dlv to stop when I reach the correct test. will it be possible to add support for cond in gdlv?. Not having cond is the only blocker for me to switch from cli dlv to gdlv. I'm sure I can't be the only one :)

[aarzilli]

You can set a condition by right clicking on a breakpoint, selecting "Edit breakpoint" and setting the "Condition" field.

[gozes]

I would much rather use the command :) because usually don't set the breakpoint and then add the condition but use cond to set the breakpoint for me when the condition is met