Bump flagd version and add telemetry support

[askpt]

This pull request updates the flagd resource integration to use a newer container image version and adds support for OTLP exporter configuration. It also ensures the related tests reflect the image version change.

Container image update:

• Updated the flagd container image tag from v0.12.9 to v0.13.1 in FlagdContainerImageTags and corresponding test assertions to ensure the latest features and fixes are used. [1] [2]

Feature enhancement:

• Added .WithOtlpExporter() to the AddFlagd resource builder, enabling OTLP exporter support for telemetry out of the box.

PR Checklist

• Created a feature/dev branch in your fork (vs. submitting directly from a commit on main)
• Based off latest main branch of toolkit
• PR doesn't include merge commits (always rebase on top of our main, if needed)
• Tests for the changes have been added (for bug fixes / features) (if applicable)
• Contains NO breaking changes
• Every new API (including internal ones) has full XML docs
• Code follows all style conventions

Other information

This is just a bump on the flagd container. It doesn't bring any breaking changes.

[Copilot]

Pull request overview

This pull request updates the flagd feature flag integration to use the latest container image version (v0.13.1) and adds built-in telemetry support through OTLP exporter configuration.

Key changes:

• Bumped the flagd container image from v0.12.9 to v0.13.1 to leverage the latest features and fixes
• Added .WithOtlpExporter() to enable OpenTelemetry integration out-of-the-box, following the established pattern used across other integrations in the toolkit

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/CommunityToolkit.Aspire.Hosting.Flagd/FlagdContainerImageTags.cs	Updated container image tag constant and XML documentation from v0.12.9 to v0.13.1
src/CommunityToolkit.Aspire.Hosting.Flagd/FlagdBuilderExtensions.cs	Added .WithOtlpExporter() call in the AddFlagd method to enable OTLP telemetry exporter support
tests/CommunityToolkit.Aspire.Hosting.Flagd.Tests/AddFlagdTests.cs	Updated test assertion to expect the new v0.13.1 container image tag