Update makefile for go-mod downloads

[pravarag]

What type of PR is this?

/kind feature

What this PR does / why we need it:

As part of this change, we are adding an entry into the Makefile to include go-mod downloads so that those can be referred into prow job configs.

Which issue(s) this PR fixes:

Fixes #56

Special notes for your reviewer:

This is a WIP PR

/label tide/merge-method-squash

[sanposhiho]

Looks good.

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: pravarag, sanposhiho

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[sanposhiho]

@pravarag
Do you want to add more change to this PR? If not, feel free to open it.
(I approved it, so it should be merged when it is opened.)

[pravarag]

@pravarag Do you want to add more change to this PR? If not, feel free to open it. (I approved it, so it should be merged when it is opened.)

Thanks, though I'm still looking for ways to test the integration if that's possible. Otherwise will open this and other PR to be merged.