Add example for building an external secondary index for parquet files #27356

Job	Run time
cargo check	3m 38s
cargo test (win64)	33m 12s
Check cargo fmt	38s
build with wasm-pack	2m 9s
cargo test (macos)	8m 58s
cargo test (macos-aarch64)	10m 26s
Verify Vendored Code	51s
Verify MSRV (Min Supported Rust Version)	6m 20s
cargo examples (amd64)	12m 19s
cargo test (amd64)	9m 34s
cargo test hash collisions (amd64)	9m 13s
clippy	5m 2s
cargo doc	3m 52s
cargo test datafusion-cli (amd64)	3m 29s
cargo test doc (amd64)	11m 59s
Run sqllogictest with Postgres runner	2m 58s
cargo test pyarrow (amd64)	2m 32s
verify benchmark results (amd64)	10m 12s
check Cargo.toml formatting	2m 46s
check configs.md is up-to-date	2m 22s
	2h 22m 30s

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