Create pre-release workflow for Vale VSCode extension

[Copilot]

Overview

This PR implements a complete pre-release publishing flow for the Vale VSCode extension, addressing the different ways Microsoft Visual Studio Marketplace and Open VSX Registry handle pre-release versions.

Problem

Previously, the extension only had workflows for stable releases. There was no way to publish pre-release versions (alpha, beta, or release candidate) to allow users to test new features before stable releases.

Solution

This implementation adds dedicated pre-release workflows while maintaining backward compatibility with the existing stable release process.

New Workflows

publishPreRelease.yml

• Publishes to both Open VSX Registry and Microsoft Marketplace with the preRelease: true flag
• Triggers on tags matching: *-alpha*, *-beta*, or *-rc*
• Example tags: v0.31.0-beta.1, v1.0.0-rc.1, v0.31.0-alpha.1

preRelease.yml

• Creates GitHub pre-releases with auto-generated release notes
• Triggers on the same tag patterns as above

Updated Workflows

Both publishTags.yml and release.yml now exclude pre-release tags using negation patterns, ensuring stable releases and pre-releases are handled independently:

tags:
  - "*"
  - "!*-alpha*"
  - "!*-beta*"
  - "!*-rc*"

Tag Naming Convention

Stable releases: vX.Y.Z (e.g., v0.31.0)

• Triggers stable release workflows

Pre-releases: vX.Y.Z-{alpha|beta|rc}[.N] (e.g., v0.31.0-beta.1)

• Triggers pre-release workflows

How It Works

Both marketplaces (Microsoft and Open VSX) support pre-release versions using the same mechanism (preRelease: true parameter), making the implementation consistent across both platforms. Users can opt-in to pre-releases through VS Code's extension UI by switching to the pre-release channel.

Documentation

• Updated CONTRIBUTING.md with comprehensive pre-release publishing instructions
• Added pre-release workflow status badge to README.md

Benefits

• ✅ Safe testing of new features before stable release
• ✅ User choice to opt-in to pre-releases
• ✅ Automated publishing with no manual intervention
• ✅ Consistent behavior across both marketplaces
• ✅ Clear tag naming convention

Validation

• All YAML files validated for syntax correctness
• Tag pattern logic tested with multiple tag formats
• No conflicts between stable and pre-release workflows
• Backward compatible with existing release process

Fixes #[issue_number]

Original prompt

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This section details on the original issue you should resolve

<issue_title>Create pre-release flow</issue_title>
<issue_description>The Microsoft and VSX stores handle pre-releases in different ways, so to handle pre-releases in the future, there needs to be a new workflow.</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #76

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