fix: make full use of nightly build functionality by publishing github releases and not tagging docker images as latest

[obs-gh-mattcotter]

Description

The objective of this change is to create github releases and publish docker images whenever we do a nightly build, but not tag either as latest (and instead use tag dev-nightly). Before this change: no github releases were published, and docker builds were published and tagged latest.

Checklist

• Created tests which fail without the change (if possible)
• Extended the README / documentation, if necessary

[obs-gh-mattcotter]

We only advertise installing on windows via zip + powershell script. These msi files are published in our releases currently, but afaik they are never used, so let's save some work and reduce complexity

[obs-gh-mattcotter]

We install on mac via zip and don't use the homebrew install. This currently isn't published, just built when running release and then ignored.

[obs-gh-mattcotter]

I believe that I can run this workflow before merging, but I will wait until the changes get approved to do so.

[obs-gh-mattcotter]

@obs-gh-alexlew this seems to be working: https://github.com/observeinc/observe-agent/releases/tag/dev-nightly

[obs-gh-mattcotter]

I verified also that docker tags look good:
https://hub.docker.com/r/observeinc/observe-agent/tags

[obs-gh-alexlew]

why is this part necessary?

[obs-gh-mattcotter]

Github releases are based on git tags. I think we always need a git tag in order to create a GH release. This step updates the dev-nightly tag to the commit from which we are building the release. To keep our releases clean, I figured it would be nice to just have a single nightly tag (I believe this is how the goreleaser repo handles nightly release).