Semantic Versioning for BACK Stack Releases

We should implement a workflow for semantic versioning of the BACK stack components to clarify the differences between releases and targets for end users.

Suggested workflow:
- Changes to the `main` branch result in a new release candidate for the next semantic minor version.
- The current version is `0.1.0`, so changing the main branch will result in the `0.2.0-rc.1` tag. The next change will result in `0.2.0-rc.2`, and so on.
- Once ready, we will cut a new release (manually trigger for now).
- So if `0.2.0-rc.2` is the current release candidate, we will release `0.2.0`.

This should be (relatively) simple to implement with a GitHub workflow. The existing [`release` workflow](https://github.com/back-stack/showcase/blob/main/.github/workflows/release.yaml) cuts a new tag with the commit sha for each push to the `main` branch. This should be modified so that the `release` workflow handles generated the new version tag and then build steps are moved to a new `build` workflow that is triggered by the creation of a new tag.

Comienza con .github/workflows/release.yaml e inspecciona cómo los pushes a main crean actualmente etiquetas commit-SHA e invocan pasos de build. Separa los pasos de build en un nuevo workflow de build activado por la creación de una etiqueta y, después, verifica que main produzca etiquetas secuenciales de release-candidate con versión semántica y que el release manual produzca la etiqueta final correspondiente.

Escrito por el modelo de indexación a partir del texto del issue.