ci: publish :latest tag on release for fairvisor-edge and fairvisor-cli

## Problem

The release workflow only pushes versioned tags (`v0.1.0`) and SHA tags. No `:latest` tag is published. Documentation references `ghcr.io/fairvisor/fairvisor-edge:latest` which currently does not exist in GHCR.

## Fix

Add `:latest` to the tags in `docker/build-push-action` for both images in `.github/workflows/release.yml`.

Fixed in PR #70.