Allow more control over PR comment resolution trailers

### Description

Users should have more control over the attribution trailer added when Copilot resolves a PR review comment, including its wording, presentation, and whether it is included.

### Example

When a user identifies a review comment and explicitly asks Copilot to address it, the resulting comment currently includes a prominent note stating:

> Auto-resolved by the GitHub Copilot app.

In this case, “auto-resolved” is inaccurate because the user initiated the resolution. The note and icon are also unnecessarily prominent; a concise one-line trailer would be sufficient.

### Expected behavior

The trailer should accurately distinguish between user-prompted and agent merge PR comments. Its formatting should remain lightweight, with an option to customize or disable it.

Das Issue nennt keine Dateien, Tests oder Einstiegspunkte; beginne damit, den Copilot-Fluss zur Auflösung von PR-Kommentaren und die Stelle zu finden, an der sein Attributions-Trailer erzeugt wird. Erledigt bedeutet, dass durch Benutzer angestoßene und durch den Agenten initiierte Auflösungen unterschieden werden, die Darstellung zurückhaltend ist und Benutzer den Trailer anpassen oder deaktivieren können.

Vom Indexierungsmodell aus dem Issue-Text verfasst.