Separate declarative steps generation from main class

The main class of the Pipeline Steps Documentation Generator codebase contains some functions that are required exclusively for generating declarative steps documentation. Thus, it makes sense to move these functions to a new class that is dedicated to declarative steps.

There are two benefits of doing this: 

1. The main class becomes less crowded with specific use-case functions and variables making it more readable.
2. All related functions are shifted to another class, making it easier to remove the generation of the declarative steps if the need arises.