Keep the type when entire of the field should be replaced

[YaSuenag]

Types of changes

• Enhancement (project structure, spelling, grammar, formatting)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

A description of the changes proposed in the Pull Request

We've introduced to replace placeholders with environment variable or parameters in inputs, but the replacement enforces string type. For example timestamp as Date would be string without JSON.strigify(), it makes incorrect parameter in HTTP request body in JSON.
This PR keeps original type if entier of parameter are needed to be replaced. Note that the result would be string if the replacement happens as a part of string like aaa ${env.BBB} ccc`.