feat: update block plugin settings visibility

[MohamedAliBouhaouala]

Motivation

The following PR updates block settings visibility to private in order to avoid confusion between default block settings and block args.

Fixes # (598)

Type of change:

Please delete options that are not relevant.

• 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 not work as expected)
• This change requires a documentation update

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added unit tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes