Add StorageEngine type to StorageMetrics trace events

[sfc-gh-satherton]

Add StorageEngine type to StorageMetrics trace events.
Also hardcoded storage engine types as they must not change.

This will also be cherry picked to the 7.1 branches.

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[fdb-windows-ci]

Doxense CI Report for Windows 10

• Commit ID: 03df62e
• Result: ✔️ SUCCEEDED
• Build Logs (available for 30 days)

[foundationdb-ci]

Result of foundationdb-pr-macos on macOS BigSur 11.5.2

• Commit ID: 03df62e
• Duration 0:40:12
• Result: ✅ SUCCEEDED
• Error: N/A
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[foundationdb-ci]

Result of foundationdb-pr-cluster-tests on Linux CentOS 7

• Commit ID: 03df62e
• Duration 0:41:44
• Result: ❌ FAILED
• Error: Error while executing command: tar -czf "${CODEBUILD_SRC_DIR}/packaging/docker/website/${FDB_VERSION}/fdb_${FDB_VERSION}.tar.gz" --directory "${CODEBUILD_SRC_DIR}/packaging/docker/website/${FDB_VERSION} .. Reason: exit status 2
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[foundationdb-ci]

Result of foundationdb-pr on Linux CentOS 7

• Commit ID: 03df62e
• Duration 0:58:44
• Result: ✅ SUCCEEDED
• Error: N/A
• Build Logs (available for 30 days)