feat: add opt-in bulk entry operations to space import

[Esteban Fernandez (efgalione)]

Summary

Adds an opt-in bulk entry import path for large Contentful restores, as proposed in #3331.

The new --use-bulk-entries flag:

• Keeps content models, locales, tags, editor interfaces, and assets on the existing contentful-import path
• Creates and updates entries through Bulk Entry Operations in batches of up to 10,000
• Publishes previously published entries through Bulk Actions in batches of up to 200
• Preserves --skip-content-updates, --skip-content-publishing, and --content-model-only
• Reports an actionable error when Bulk Content Operations is not enabled

The existing import behavior remains unchanged unless the flag is explicitly enabled.

Design

• Partitions entries into create and update groups using destination IDs and versions
• Uses environment-scoped uploads
• Polls asynchronous operations until completion or failure
• Handles per-entry failures from completed bulk jobs
• Runs bulk entry jobs sequentially because only one may be active per space
• Does not silently fall back to classic entry imports after an entitlement error
• Documents the decisions and trade-offs in an ADR

Usage

contentful space import \
  --space-id '<space-id>' \
  --environment-id '<environment-id>' \
  --content-file './export.json' \
  --use-bulk-entries