Add mapping feature

[manushak]

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

• add mapping to the manifest schema.
• to test add a mapping block like this

mapping:  
   'parameter-name-in-the-plugin': 'parameter-name-in-the-input'

[narekhovhannisyan]

are there cases where mapping is used?

[manushak]

I'll add use cases for every unit test

[narekhovhannisyan]

its not clear where the mapping should be. f.ex. in plugin settings or in context

[manushak]

yeah, you're right. In this case, I think it will be good to remove from the plugin's readme file