feat(clickpipes): add advanced CDC table mappings

[sdairs]

MySQL, MongoDB, and BigQuery CDC creates can now send the full table-mapping objects supported by ClickHouse Cloud through repeatable --table-mapping-json flags. Simple --table-mapping values remain supported and can be mixed with JSON mappings; requests preserve simple-first ordering, optional and explicitly empty values, MySQL partitionKey versus partitionByExpr, and BigQuery mappings for both service-account and workload-identity authentication.

The CLI strictly validates each source-specific object before reading credential or CA files or issuing an HTTP request. It rejects malformed JSON, unknown fields and engine values, missing or blank identifiers, contradictory custom-sorting settings, blank array entries, and duplicate MySQL arrays. The preceding API prerequisite exposes analyzer-checked engine value lists for CLI validation.

Documentation now includes complete examples for all three sources and explains table engines, sorting-key behavior, and the two MySQL partition fields.

Validation:

• cargo fmt --all --check
• cargo clippy -p clickhousectl -- -D warnings
• cargo test -p clickhousectl (1,085 unit tests passed, 1 ignored; 319 cloud request-shape tests passed, 1 ignored; all local and telemetry binaries passed)
• cargo check -p clickhousectl --no-default-features
• cargo clippy -p clickhousectl --all-targets --no-default-features -- -D warnings
• cargo clippy -p clickhouse-cloud-api -p clickhouse-openapi-analyzer --all-targets -- -D warnings
• cargo test -p clickhouse-cloud-api -p clickhouse-openapi-analyzer
• python3 -m unittest discover -s scripts/tests -p 'test_*.py' (90 tests passed in the aggregate; the sole sandbox-blocked temporary-Git fixture passed on an exact outside-sandbox rerun)

Closes #691