Clarify aladino and engine mocks

[ferreiratiago]

Is your feature request related to a problem? Please describe.
Currently, both aladino and engine provide mocks for pull request details.

If you open engine/mocks.go you will see that it has the function GetDefaultMockPullRequestDetails which is also provided on lang/aladino/mocks.go.

This can be a bit confusing as to what mock function should be called.

Describe the solution you'd like
In this issue we would like to address:

• Investigate the need for both function
  • If both are required then name them differently and document the explanation for both to exist.
• Investigate if there are some other functions that may bring confusion or aren't really necessary.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Please provide the output of the investigation in the issue discussion.