Dev window release version prep

[brianeray]

Background

We're trying to do four things with this PR:

• Adding more structure around development windows by setting up explicitly for the next releases of generator and module plugin subprojects.
• Correct outdated non-build version references, especially version references from generator code to the module plugin. (See e.g. Gradle error on fresh generated module skeleton #49, which is likely caused by stale plugin version references.)
• Identify all such references in the sources as a guide for future releases. And perhaps some day automated update by, e.g., Gradle tasks and/or GitHub release workflows.
• Sync versioning across all projects contained in this monorepo.

Changes

Prepare for upcoming releases of both generator and plugin.

• Generator core and CLI: 0.1.0-SNAPSHOT > 0.4.0-SNAPSHOT.
• Module plugin: 0.3.0 > 0.4.0-SNAPSHOT.

Generator currently only scoped for bug fixes, but syncing its version with that of the module plugin for ease of maintenance. Module plugin has bug fixes and an improvement, hence the minor version bump.

generator and gradle-module-plugin are included builds, not subprojects, so there's not an easy way to just set a single version from the root build script.

With fixes for dangling old version strings throughout, especially for generator sources referencing the module plugin version.

These will become 0.4.0 before we release.

Reviewer Notes

Artifacts for these -SNAPSHOT versions may or may not be published. In that sense they may break the generator-core and generator-cli subprojects. Generating publically-available snapshot artifacts is not the goal of this PR.

[brianeray]

Recommended by an off-GH review: Going to sync the generator versions with the module version for simplicity. The two have marched and can march to their own cadence but the ease of maintenance outweighs "wasting" a version on one or the other. Let's just make them the same version.

[brianeray]

Confirming the Reviewer Notes, the release.yml workflow can't even push a -SNAPSHOT version of the plugin:

> Task :publishPlugins FAILED
Could not reuse POM from pluginMaven publication because mavenCoordinates() was used
Publishing plugin io.ia.sdk.modl version 0.4.0-SNAPSHOT

 ...

* What went wrong:
Execution failed for task ':publishPlugins'.
> Failed to post to server.
  Server responded with:
  Version must not end with '-SNAPSHOT'

Not going to worry about this for now; in fact it's a nice guard during the 0.4.0 dev window.