Add go.mod file to define dependencies

[c0d1ngm0nk3y]

• Read the Contributing document.

Summary

To install the locket cli, we call go install code.cloudfoundry.org/locket/cmd/locket@latest. But currently this is not possible because the dependencies are not managed. Adding a go.mod and a go.sum file will define the used dependencies.

Backward Compatibility

Breaking Change? No

[MarcPaquette]

To reiterate the comments mentioned

@c0d1ngm0nk3y ,

We do have long term plans to change the way we go mod'd our release, but at this time we're in a bit of a tangled web. Putting a go.mod on this repo would have consequences elsewhere in a way that we're not fully ready to deal with yet.

We understand this is not an ideal scenario.