Allow output template changes for single-target mode

[SuperQ]

Is your feature request related to a problem? Please describe.

For --single-target builds where the user wants to just get a binary output, it would be nice to be able to override the dist and name_template. This way our project can have a simple make build that outputs a ./project_name binary.

Describe the solution you'd like

A configuration option like this:

single_target:
  destination: './'
  name_template: "{{ .Binary }}"

Describe alternatives you've considered

We could have a post-build script that moves the dist/binary_name into the local dir, but I think it would be cleaner if the single-target mode moved the built binary into place.

Additional context

This would help with the transition away from the Prometheus promu builder.

[SuperQ]

@caarlos0 Not sure how involved this would be. Or if it would be better to build the binary directly to the target location, or build and mv.

[caarlos0]

I need to take a look, but I was thinking that maybe when using --single-target we could build to . by default (or move after built automatically) and also name the binary as go build would... 🤔

OR, accept a -o flag like go build does...

[caarlos0]

what do you think about #2701 @SuperQ ?