Add comprehensive introduction to parametrizations tutorial

[patrocinio]

Addresses feedback that parametrization is not a well-known topic. Added introductory section that explains:

• What parametrizations are (transformations applied to parameters)
• Why they are needed (enforcing constraints like orthogonality)
• What problems they solve (hard constraints, optimization, regularization)
• Real-world motivation with concrete examples
• References for further reading (key papers and resources)

This provides essential context for beginners before diving into examples.

Fixes #3581

Description

Checklist

• [ ] The issue that is being fixed is referred in the description (see above "Fixes #ISSUE_NUMBER")
• [ ] Only one issue is addressed in this pull request
• [ ] Labels from the issue that this PR is fixing are added to this pull request
• [ ] No unnecessary issues are included into this pull request.