feat: Add `draft` custom query property and treat `wip` as an alias

Description

Some time ago, GitLab renamed WIP: MR status to Draft:. The VSCode extension Custom Query configuration still uses wip.

This MR adds a new custom query property, draft, which acts as an alias for wip.

The default value for wip has been removed, and now when building the custom query the extension will use wip || draft to allow either property to be used.

Both properties still map to the same wip API parameter.

Related Issues

Resolves #540 (closed)

How has this been tested?

In settings.json -> gitlab.customQueries add a custom query:

    {
      "name": "Custom query - my draft MRs",
      "type": "merge_requests",
      "scope": "assigned_to_me",
      "noItemText": "No draft merge requests assigned to you.",
      "state": "opened",
      "draft": "yes"
    }

Can test various combinations of wip/draft being yes or no

Screenshots (if appropriate)

What CHANGELOG entry will this MR create?

• fix: Bug fix fixes - a user-facing issue in production - included in changelog
• feature: New feature - a user-facing change which adds functionality - included in changelog
• BREAKING CHANGE: (fix or feature that would cause existing functionality to change) - should bump major version, mentioned in the changelog
• None - other non-user-facing changes

Closes #540 (closed)