feat: Implement list and discard for workerpools queue

[jchanam]

Description

Adds workerpool worker queue command to manage runs in a worker pool’s schedulable queue from the CLI:

• queue list shows queued runs (table or JSON).
• queue discard supports a single run via --stack and --run, or bulk discard with the same filters as list plus --yes to confirm.

Uses searchSchedulableRuns on publicWorkerPool (no --pool-id) or workerPool(id: …) for a private pool, and runDiscard(stack:, run:) for discard. API search predicates include isPrioritized, state, and type; --stack, --drift-detection, and --commit are applied client-side after paging results so --limit still applies for bulk discard when those filters are used.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe):

Changes Made

• New subcommands: spacectl workerpool worker queue list and spacectl workerpool worker queue discard
• internal/cmd/workerpools/queue.go — GraphQL queries, list/discard actions, collectSchedulableRuns (pagination + client-side filters), API-only predicates in buildAPISchedulableRunPredicates
• internal/cmd/workerpools/cmd.go — command registration
• internal/cmd/workerpools/flags.go — queue-related flags and help text

Testing

• I have tested these changes locally
• I have added/updated tests as needed
• All existing tests pass (go test ./...)

Screenshots (if applicable)

N/A (CLI only).

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have commented my code where necessary
• My changes generate no new warnings

Related Issues

Closes #
Fixes #
Related to https://feedback.spacelift.io/p/allow-manage-runs-with-spacectl