CLI: generate `has_one` relation for foreign key of unique index / constraint #4302

Job	Run time
Init	3s
Rustfmt	15s
Clippy	1m 30s
Examples (examples/actix_example)	1m 38s
Unit Test	1m 43s
Examples (examples/axum_example)	1m 38s
Examples (examples/basic)	1m 18s
Examples (examples/graphql_example)	1m 38s
Examples (examples/jsonrpsee_example)	1m 37s
Examples (examples/loco_example)	1m 38s
Examples (examples/loco_starter)	1m 38s
Examples (examples/poem_example)	1m 36s
Examples (examples/proxy_gluesql_example)	1s
Examples (examples/rocket_example)	1m 27s
Examples (examples/rocket_okapi_example)	1m 39s
Examples (examples/salvo_example)	1m 48s
Examples (examples/seaography_example)	1m 17s
Examples (examples/tonic_example)	1s
Compile SQLite (async-std, native-tls)	1s
Compile MySQL (actix, native-tls)	1s
Compile SQLite (async-std, rustls)	1s
Compile PostgreSQL (tokio, native-tls)	1s
Compile MySQL (actix, rustls)	1s
CLI	0s
Compile PostgreSQL (tokio, rustls)	1s
Issues Matrix	0s
Issues	0s
MySQL	1s
MariaDB	1s
SQLite	1s
Postgres	1s
	22m 35s

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