Add update-hack knobots action

[upodroid]

Part of knative/infra#134
For now, only test-infra is being synced.

/cc @dprotaso @kvmware

[knative-prow]

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[krsna-m]

Doesn't upgrade deps job do this? knative/test-infra@0486b3e#diff-33ef32bf6c23acb95f5902d7097b7a1d5128ca061167ec0716715b0b9eeaa5f6R30

[upodroid]

Not quite. knative/hack is currently distributed as a vendored go module. When we get rid of vendor, we need to distribute it in a different way which will be done by update-hack action.

[krsna-m]

As per the feedback from our WG share out, a proposal needs to be written and agreed upon before we rip out vendor. Let's get everyone on the same page before we start making changes?

[upodroid]

I remember, if we merge this as is, it would only run against test-infra which is fine. We don't release anything from that repo.

Working on the proposal doc.

[krsna-m]

closing this now until there is a proposal doc and the infra/toolbox spit is done.