Support multiple init scripts and measure their hashes

[kvinwang]

Motivation

Infrastructure and cloud providers need to contribute initialization code that can be approved by multiple parties. Measuring each script separately lets every party verify its own approved code directly from attestation evidence without reconstructing and parsing the complete compose document. The per-script hashes are additional transparency measurements; compose-hash remains the authoritative measurement of the complete application configuration.

The five-script limit bounds runtime-event-log and MrConfigV3 growth while allowing several independently approved infrastructure initialization stages.

Summary

• accept init_script as a string, an array of strings, or null, with a maximum of five scripts
• require manifest v3 for multiple scripts and reject unsupported images in the UI before deployment
• execute array entries in order while preserving multiline script boundaries
• preserve compatibility by serializing exactly one script as a string and multiple scripts as an array
• emit one ordered init-script-hash runtime event per script immediately after compose-hash
• model MrConfigV3 init_script_hashes as optional: omission disables the check, while an explicit empty list requires no init scripts
• when present, compare the MrConfigV3 list with hashes recomputed inside the guest
• bind the list through SEV-SNP HOST_DATA and expose it through verified AppInfo
• expose ordered hashes as optional values through AppInfo.init_script_hashes and decode_init_script_hashes(), preserving missing versus explicit empty lists
• stop runtime-event hash collection at system-ready, excluding application-controlled events appended after boot
• share one validated hash-list serde implementation from dstack-types
• show scripts in separate VMM UI text areas with add/remove controls and enforce the five-script UI limit
• fix gateway_enabled flatten serialization so AppCompose serialization is directly tested
• update TDX, SNP, AWS, tutorial, and security-boundary documentation

Testing

• cargo test -p dstack-types
• cargo test -p dstack-util config_id_verifier
• cargo test -p dstack-util test_multiple_init_scripts_require_v3_manifest
• cargo test -p dstack-attest
• cargo test -p dstack-vmm mr_config
• cargo check -p dstack-vmm -p dstack-util -p dstack-attest -p dstack-verifier
• npm run build in dstack/vmm/ui
• bash -n os/common/rootfs/dstack-prepare.sh
• git diff --check

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