docs(recipes): rewrite suites recipe, reference unit unit testing docs

[omermorad]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/docs.nestjs.com/blob/master/CONTRIBUTING.md

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Docs

What is the current behavior?

The existing recipe does not accurately reflect the current state of the library. Suites has matured significantly, and the documentation needed a rewrite to represent the library capabilities more accurately. The previous version used overly complex examples, lacked clarity, and did not provide sufficient context on when to use suites versus other testing approaches.

Issue Number: N/A

What is the new behavior?

This pull request rewrites the recipe to accurately reflect the current state of the library.

• Uses simplified, focused examples appropriate for mid-level developers
• Demonstrates both TestBed.solitary() and TestBed.sociable() patterns
• Properly positions Suites alongside Test.createTestingModule() with clear guidance on when to use each
• Adds a cross reference in /content/fundamentals/unit-testing.md (auto mocking section)
• References createMock from @golevelup/ts-jest as a parallel alternative

Added a cross reference in /content/fundamentals/unit-testing.md (auto mocking section) that mentions Suites as an alternative for focused unit testing with automatic mock generation

Does this PR introduce a breaking change?

• Yes
• No