[eas-cli] Add --skip-screenshots and --skip-previews flags to metadata commands

[TimBroddin]

Why

eas metadata:pull downloads every screenshot and video preview from App Store Connect, and eas metadata:push syncs them back. When you only want to manage textual metadata (descriptions, keywords, review info, etc.), downloading/uploading all media assets is slow and unnecessary. This PR adds opt-out flags for both asset types.

How

• Added a --skip-screenshots and a --skip-previews flag to both eas metadata:pull and eas metadata:push.
• The flags are threaded through downloadMetadataAsync / uploadMetadataAsync to createAppleTasks(), which now filters out the ScreenshotsTask and/or PreviewsTask. Skipping the task entirely also avoids the per-locale screenshot/preview set fetches in prepareAsync.
• Because push deletes remote video previews whose types are missing from the store config, metadata:pull --skip-previews logs a warning that pushing the generated config without --skip-previews would delete remote previews. (Screenshots have no such cleanup pass, so mixing the screenshot flag between pull and push is safe.)
• Regenerated the oclif README and added a changelog entry.

Test Plan

• New unit tests for createAppleTasks filtering (packages/eas-cli/src/metadata/apple/tasks/__tests__/index.test.ts) and for flag pass-through in download.test.ts / upload.test.ts.
• Full metadata suite passes: 16 suites, 197 tests.
• Verified bin/run metadata:pull --help and bin/run metadata:push --help show the new flags.
• yarn typecheck, yarn lint, and yarn fmt:check pass.

[github-actions]

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File Patterns	Mentions
**/*	@douglowder
packages/eas-cli/src/metadata/**	@byCedric
packages/eas-cli/src/commands/metadata/**	@byCedric

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