Add benchmark CLI entry point

[tkilias]

Goal

Expose benchmark artifact tooling through a Click-based executable.

Scope

• Add click as a runtime dependency.
• Add the pytest-exasol-benchmark executable.
• Define package, compare, and store command skeletons only.
• Do not add a command that runs pytest or benchmarks.

Acceptance Criteria

• All three commands are discoverable through CLI help.
• Required arguments are validated with clear errors.
• The package metadata exposes the executable.