Add simple file-based app for rendering frequent announcement templates

[lbussell]

This PR adds a simple file-based app that we can use to easily render some frequently-posted announcements.

The app:

• Supports multiple templates so adding more is easy
• Prompts the user interactively for template inputs
• Can use smart defaults (like defaulting to patch Tuesday dates that line up with our policies, etc.)

[Copilot]

Pull request overview

This PR introduces a file-based template rendering tool for creating standardized announcements. The tool uses the Fluid templating engine with Spectre.Console for interactive prompts and includes smart defaults for common scenarios like patch Tuesday dates.

Changes:

• Added Render.cs script using C# script format with package directives
• Added alpine-floating-tag-update.md template with Fluid syntax for Alpine version update announcements

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
.github/announcement_templates/Render.cs	C# script that parses templates, prompts users for input with defaults, and renders announcements using Fluid templating
.github/announcement_templates/alpine-floating-tag-update.md	Fluid template for Alpine floating tag update announcements with parameterized version and date information

[mthalman]

I question the location of these files. It seems like they should belong within the eng directory.

[lbussell]

I question the location of these files. It seems like they should belong within the eng directory.

Good point. I was thinking like issue_templates, but the .github folder should only contain things used directly by GitHub. It fits in eng/ with readme-templates and dockerfile-templates. 3984cf9

[lbussell]

Check markdown links workflow says:

Cannot reach https://support.microsoft.com/contactus/ Status: 500

False positive and also not related to this PR.

[lbussell]

Blocked by Test agents sometimes run out of space during PR validation (dotnet/dotnet-docker#6906)