docs: Add ClickHouse scaler documentation

[krasnosvar]

Description

This PR adds documentation for the new ClickHouse scaler introduced in kedacore/keda#7404.

What does this PR do?

• Adds documentation for the clickhouse scaler in version 2.19
• Documents connection options (connection string and individual parameters)
• Provides examples with TriggerAuthentication
• Documents all metadata parameters and authentication options
• Follows the same documentation pattern as PostgreSQL, MySQL, and MSSQL scalers

Documentation Added

• Trigger Specification: Complete description of the clickhouse trigger
• Connection Options: Both connection string and individual parameter configurations
• Authentication Parameters: Connection string and password authentication methods
• Examples: Multiple examples including TriggerAuthentication usage
• Parameter Documentation: All metadata parameters with descriptions and defaults

Example Usage

The documentation includes examples for:

• Using connection string from environment variable
• Using individual connection parameters (host, port, username, password, database)
• Using TriggerAuthentication with connection string
• Using TriggerAuthentication with individual parameters

Checklist

• Documentation follows the scaler documentation guidelines
• Added to correct version (2.19 - unreleased)
• All parameters documented with proper format
• Examples provided for common use cases
• Commits are signed with Developer Certificate of Origin (DCO)

Related

• Main KEDA PR: kedacore/keda#7404

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