fix(cli): omit unset ClickPipe create booleans

[sdairs]

ClickPipe creates previously replaced omitted booleans with false. That made every non-Kafka create containing another settings flag serialize the rejected Kafka-only kafka_read_committed key, and it prevented minimal creates from omitting source.validateSamples as intended.

The create builder now carries both optional booleans through unchanged: omitted values stay absent, while explicit true and false remain present. Real-binary request tests cover exact Kafka true/false payloads, minimal omission, and kafka_read_committed omission for object-storage, Kinesis, and Pub/Sub creates that contain other settings. The README documents both omission rules and the existing PostgreSQL/MySQL sample-validation no-op.

Validation:

• cargo fmt --all
• cargo clippy -p clickhousectl -- -D warnings
• cargo check -p clickhousectl --no-default-features
• cargo clippy -p clickhousectl --all-targets --no-default-features -- -D warnings
• cargo test -q -p clickhousectl (1,727 passed, 0 failed, 2 ignored)
• cargo check --workspace --all-features

Closes #595.

[iskakaushik]

LGTM