Extract the ClickPipes clap contract and parsing tests

[sdairs]

Closes #386

Summary

• Move all ClickPipes command enums, argument structs, possible values, and parsing coverage into the ClickPipes domain module.
• Preserve the boxed top-level command shape and all existing cloud::cli::* re-exports.
• Pin commands, flags, defaults, repeatability, constraints, accepted values, and top-level write classification through the real CLI parser.
• Leave ClickPipes runtime handlers, builders, output, and client wrappers unchanged for the following stack layer.

Tests

• cargo fmt --all
• cargo check --workspace --all-features
• cargo test -p clickhousectl
• cargo clippy -p clickhousectl --all-targets -- -D warnings

[Copilot]

Pull request overview

This PR refactors the ClickPipes CLI surface by relocating the entire ClickPipes clap contract (subcommands, argument structs, accepted-value sets, and parsing/write-classification tests) into a dedicated cloud::clickpipes domain module, while preserving the existing crate::cloud::cli::* public paths via re-exports.

Changes:

• Added a new crates/clickhousectl/src/cloud/clickpipes.rs module containing all ClickPipes clap enums/args, possible-value constants, and adjacent parsing + write-classification tests.
• Updated cloud::cli to re-export the moved ClickPipes types and to delegate CloudCommands::is_write_command() ClickPipe classification to ClickPipeCommands::is_write().
• Wired the new module into cloud/mod.rs so the domain module is compiled and available for the existing re-export surface.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
crates/clickhousectl/src/cloud/mod.rs	Registers the new clickpipes module in the cloud domain.
crates/clickhousectl/src/cloud/clickpipes.rs	New ClickPipes clap contract + exhaustive parsing/write-classification tests colocated with the definitions.
crates/clickhousectl/src/cloud/cli.rs	Re-exports ClickPipes types from the new module and simplifies write-classification by delegating to ClickPipeCommands::is_write().

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[iskakaushik]

LGTM