Add the Docker Compose Detector

[jpinz]

This pull request introduces a new detector for Docker Compose files, improves Docker image reference parsing, and enhances documentation. The main changes are the addition of the DockerComposeComponentDetector (default-off), refactoring of Dockerfile detection logic to use new utility methods, and updates to documentation to describe the new detector and its behavior.

This is PR 1 of 3 for splitting up #1759

[github-actions]

👋 Hi! It looks like you modified some files in the Detectors folder.
You may need to bump the detector versions if any of the following scenarios apply:

• The detector detects more or fewer components than before
• The detector generates different parent/child graph relationships than before
• The detector generates different devDependencies values than before

If none of the above scenarios apply, feel free to ignore this comment 🙂

[Copilot]

Pull request overview

This PR adds a new default-off Docker Compose detector to discover Docker image references from compose YAML files, refactors shared Docker image reference parsing/registration into a common utility, and documents the new detector with supporting tests and verification resources.

Changes:

• Added DockerComposeComponentDetector (DefaultOff) with compose/override file search patterns and YAML-based image extraction.
• Introduced shared helpers in DockerReferenceUtility to skip unresolved-variable references and to safely parse/register image references.
• Added unit tests + verification resources and updated detector documentation/index.

Show a summary per file

File	Description
test/Microsoft.ComponentDetection.VerificationTests/resources/dockercompose/docker-compose.yml	Adds compose resource with multiple services + tag/digest cases for verification runs.
test/Microsoft.ComponentDetection.VerificationTests/resources/dockercompose/docker-compose.override.yml	Adds override compose resource for verification runs.
test/Microsoft.ComponentDetection.Detectors.Tests/DockerComposeComponentDetectorTests.cs	Adds unit tests covering compose patterns, registry refs, digest refs, and unresolved-variable skipping.
src/Microsoft.ComponentDetection.Orchestrator/Extensions/ServiceCollectionExtensions.cs	Registers the new Docker Compose detector in DI.
src/Microsoft.ComponentDetection.Detectors/dockerfile/DockerfileComponentDetector.cs	Switches Dockerfile detector to shared DockerReferenceUtility parsing logic and enables nullable.
src/Microsoft.ComponentDetection.Detectors/dockercompose/DockerComposeComponentDetector.cs	Implements the new Docker Compose detector using YamlDotNet to extract services.*.image.
src/Microsoft.ComponentDetection.Contracts/DetectorClass.cs	Adds DetectorClass.DockerCompose category.
src/Microsoft.ComponentDetection.Common/DockerReference/DockerReferenceUtility.cs	Adds HasUnresolvedVariables, TryParseImageReference, and TryRegisterImageReference helpers.
docs/detectors/dockercompose.md	Adds documentation for Docker Compose detector behavior and limitations.
docs/detectors/README.md	Adds Docker Compose detector to the detector documentation index.

Copilot's findings

• Files reviewed: 10/10 changed files
• Comments generated: 4

[Copilot]

Copilot's findings

• Files reviewed: 11/11 changed files
• Comments generated: 0 new

[Copilot]

Copilot's findings

• Files reviewed: 11/11 changed files
• Comments generated: 4

[Copilot]

Copilot's findings

• Files reviewed: 11/11 changed files
• Comments generated: 1

[Copilot]

Copilot's findings

• Files reviewed: 11/11 changed files
• Comments generated: 2

[Copilot]

Copilot's findings

• Files reviewed: 11/11 changed files
• Comments generated: 1

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.0%. Comparing base (b16ab9e) to head (6d054fc).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@     Coverage Diff      @@
##   main   #1785   +/-   ##
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