docs: restructure contribution guide by merging issue submission guide

Consolidate contribution documentation by renaming issue_submission_guide.adoc
to contribution_guide.adoc and merging content from the previous contribution_guide.adoc.

Changes:
- Rename issue_submission_guide.adoc to contribution_guide.adoc (CN)
- Merge roles and responsibilities section from previous contribution_guide
- Merge getting started section (GitHub account, CLA signing)
- Add ecosystem component adaptation entry in contribution types
- Add complete ecosystem component adaptation section with detailed steps
- Remove duplicate contribution_guide.adoc (EN) as it will be recreated separately

This creates a unified contribution guide that serves as the single entry point
for all contribution-related documentation in the docs site, while the www site
maintains overview and conceptual content.

Author: jiaoshuntian