Add guidance on Feature Requests vs. Detailed Feature Proposals in contributing guidelines

Summary

This PR enhances the contributing guidelines by adding a new section that clarifies the distinction between Feature Requests (GitHub Discussions) and Detailed Feature Proposals (GitHub Issues). This guidance has been added to all 17 language versions of the CONTRIBUTING.md file.

Changes

• Added a new subsection "Feature Requests vs. Detailed Feature Proposals" under the "Finding & Planning Your Contribution" section
• Updated the table of contents to include the new subsection
• Modified the existing feature submission guidance to reference the new section
• Provided clear criteria for when to use each submission type
• Added placeholder for an issue template selection image

Why this change?

Contributors often struggle to understand whether they should submit their ideas as a Feature Request in Discussions or as a Detailed Feature Proposal in Issues. This clarification will help:

• Reduce misdirected submissions
• Streamline the contribution process
• Set proper expectations for approval requirements
• Encourage community discussion for early-stage ideas

Language Support

The changes have been consistently applied across all supported languages:

• English (main)
• Catalan (ca)
• German (de)
• Spanish (es)
• French (fr)
• Hindi (hi)
• Italian (it)
• Japanese (ja)
• Korean (ko)
• Dutch (nl)
• Polish (pl)
• Portuguese-Brazil (pt-BR)
• Russian (ru)
• Turkish (tr)
• Vietnamese (vi)
• Chinese Simplified (zh-CN)
• Chinese Traditional (zh-TW)