Add dependency resolution job for maven to DS CI template v2

What does this MR do and why?

Add a dependency Resolution job for maven to the Dependency Scanning CI template v2 that attempts to automatically generate a maven.graph.json file for a project using a pom.xml.

Maven projects have no lockfile mechanism. Accurate dependency scanning requires a maven.graph.json file, which today users must generate themselves via a custom CI job. This creates friction and makes it impossible to enforce scanning policies at scale.

The solution relies on coordinating a main dependency resolution job container with the DS analyzer running as a service container:

1. The resolution job checks out the repository and signals readiness by creating a .gitlab_ds/ready_${CI_JOB_ID} file
2. The service container detects projects needing resolution and writes a shell script to .gitlab_ds/dependency_resolution.sh
3. The resolution job executes the script, which runs the appropriate resolution command per project (e.g. mvn dependency:tree for Maven), producing graph files
4. Those files are exported as artifacts and picked up by the main dependency scanning job that runs in a later stage.

This MR partially depends on Update Scan Execution Policies EXCLUDED_VARIABL... (!227899 - merged) to ensure resolution jobs can be disabled when using Scan Execution Policies.

References

• #588765 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. checkout this branch in your GDK
2. clone this project: https://gitlab.com/gitlab-org/security-products/tests/java-maven
3. adjust CI configuration to just use v2 template:

    include:
      - template: Jobs/Dependency-Scanning.v2.gitlab-ci.yml

4. Run a pipeline and confirms that:
   1. a dependency-scanning:maven-resolution job ran in .pre stage, emitting a maven.graph.json file
   2. the dependency-scanning job ran and successfully scanned this graph file.

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