Add support for Youtrack Issues/Cards

### 📋 Description

Add support for Issue Counts from JetBrains YouTrack product. Given the customization capabilities of YouTrack on a per project level a standard Open/Closed/All would not suffice. As such the filter would need to be defined as a `query` to correctly state the YouTrack search criteria. i.e. `#Unresolved Type:Bug` would be a query getting all open bugs in my project, but someone else could need `#Open Type:Issue` based on their setup.

Project is the only guarantee, so this could be used in a path routing similar to user/repo that VCS issues badges work.

### 🔗 Data

An appropriate endpoint is available at: https://www.jetbrains.com/help/youtrack/devportal/resource-api-issuesGetter-count.html

For a private project either self-hosted (depending on the level of security configured) or on their cloud solution, a token would be required.

### 🎤 Motivation

Many VCS systems now offer an 'External Issues' feature, wherein the Issues don't exist in the VCS like GitHub does, but can exist in a third party external system such as YouTrack. Gitlab/Gitea/Forgejo support this and even translate `#123` etc into correct URL's to take them directly into the external issue management tool.

Projects using this feature would not find any benefit of issues badges for the VCS they use, and would not be able to show issues as badges on their websites/readme's.

Review the existing VCS issue-badge routing patterns and the YouTrack issue-count endpoint linked in the issue. Define project-based paths, query filters such as `#Unresolved Type:Bug`, and token handling for private projects; done means badges can report the resulting counts for the supported YouTrack configurations.

Written by the indexing model from the issue text.