chore: move the aptos smoke workflow off aptos-init

[cawthorne]

Summary

• move the Aptos smoke workflow off the old aptos-init core branch
• pin the smoke workflow to the merged smartcontractkit/chainlink#21828 commit by default so runs stay stable and reproducible
• keep the PR-body override path for testing alternate core refs with the documented core_ref:<ref>; syntax
• explicitly opt the generated core TOML into mock-streams-trigger@1.0.0 so the existing workflow smoke path still works with gated core registration
• remove the stale README note that said develop could not work yet

Testing

• bash .github/actions/get-core-ref/test_get_core_ref.sh
• parsed integration-tests/templates/core.toml through the chainlink TOML types from the merged smartcontractkit/chainlink#21828 commit
• full smoke run is still blocked locally in this session because the Docker daemon is not running