Remove templated config_file path, fix parameter comments

[pavel-salnikov]

Description

Fixes the template example and comments:

• Removed the templated config_file parameter (should point at the usual config with GKE credentials)
• Updated the Airflow templates reference link
• Added the comment about templated params
• Capitalize Kubernetes, Docker
• Mention namespace param usage for Composer 3
• Namespace param is not required

Checklist

• I have followed Sample Guidelines from AUTHORING_GUIDE.MD
• README is updated to include all relevant information
• Tests pass: nox -s py-3.9 (see Test Environment Setup)
• Lint pass: nox -s lint (see Test Environment Setup)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

[kosteev]

Modulo comments about templated parameters