Publish GitLab VSCode color theme as an artifact

Issue: Publish GitLab VSCode color theme as an artifact (#301 - closed)

What does this MR do and why?

It publishes the VSCode color theme implementation used by the Web IDE as a standalone installation package. The goal of this change is using the same color themes in GitLab Workspaces instead of the default VSCode theme (see gitlab-web-ide-vscode-fork#47 (closed) for more information). The changes in this Merge Request are organized in four commits:

1. !379 (bc24b23e) moves the icons font to the vscode-extension-gitlab-vscode-theme package. We also need to publish these icons along with the theme extension so we can use them in Workspaces.
2. !379 (7b48efcd) implements a script that packages the extension as a vsix file and also adds LICENSE, README.md, and other essential files to ensure the theme extension can function as a standalone installable.
3. !379 (7922409f) Modifies the create-development-package CI job to generate a vsix artifact, and it creates a publish-gitlab-vscode-theme-package CI job that uploads the vsix artifact to the package registry, and creates a release for that package.
4. !379 (ff073da2) Updates the documentation.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

This Merge Request doesn't introduce user-facing changes.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

• To generate the vsix file, run the scripts/pack-gitlab-vscode-theme-package.sh script in your local environment.
• The job that publishes a release only runs in the main branch. I tested the job in this Merge Request by removing that condition, and this is an example of a successful execution https://gitlab.com/gitlab-org/gitlab-web-ide/-/jobs/8001652492. This is the release published by the job https://gitlab.com/gitlab-org/gitlab-web-ide/-/releases/0.0.1-dev-20241005091415.
• You can modify this MR to run the same experiment, and ensure that these changes work correctly.