The npm scripts "publish:hex" defined in sync-service and elixir-client publish on every commit to main

[alco]

When a new commit is merged to main and there are no any changesets in .changeset/ yet, the publish:hex scripts will run and try to publish to Hex using the same package version but built from a different commit.

This isn't a critical problem because publish an existing package can only succeed when the --replace flag is provided. However, we're wasting compute and prolonging the CI workflow's runtime needlessly with this setup.

https://github.com/electric-sql/electric/actions/runs/12420871198/job/34679331020

Instead we need an explicit CI workflow that will trigger new version publishing to hex.pm when it detects a new Git tag on the repo, similarly to how we need that for release builds on Buildkite - #2204.