feat: 'release pull' command implementation

[nterbogt]

release pull VERSION and release pull VERSION --service fpm commands.

[Copilot]

Pull request overview

Adds a new skpr release pull subcommand to pull the packaged container images associated with a release via the Skpr API, using existing Docker/ECR auth plumbing.

Changes:

• Introduces internal implementation for pulling release images and parsing image references.
• Adds Cobra CLI wiring for skpr release pull with an optional --service filter.
• Threads DockerClientId into the release command so the new subcommand can create the correct Docker client.

Reviewed changes

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

File	Description
internal/command/release/pull/command.go	Implements release image pulling logic (API lookup, auth selection, Docker pull, image ref parsing).
cmd/skpr/release/pull/command.go	Adds the skpr release pull Cobra command and --service flag.
cmd/skpr/release/command.go	Registers the new pull subcommand and updates NewCommand to accept DockerClientId.
cmd/skpr/main.go	Passes featureFlags.DockerClient into release.NewCommand(...).

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