Set up versioned releases

[ethan-lowman-dd]

We are still pre-1.0, but we need to give users a way to know when breaking changes are made and upgrade accordingly.

As discussed in the TUF community meeting, we intend to version pre-1.0 releases as v0.x.y, where x is incremented for breaking changes.

We will build release notes from a changelog file, updated in each PR as necessary. Changes will be tagged by sub-system, like [client], [cli], or similar.

A PR review checklist may help with the process.

[shibumi]

Note: We have a PR for releases via goreleaser and goreleaser can handle pre-releases + generate changelogs. It really makes sense to have a closer look on my PR here and maybe get this done for the first release:

#157

[shibumi]

If needed I can provide a test release in my fork, so that you can have a look at it and we discuss changes etc

[joshuagl]

Cross-referencing an older issue where the need for releases is discussed #114

[rdimitrov]

Closing this as it has been already addressed in #234

As a side note, the PR review checklist will be covered in #190

[zwass]

Glad to see that this has been addressed! Thank you!