docs: add community contribution guides

[Supull]

Fixes #6828

• Add Community-Contributing overview
• Add Reporting-An-Issue how-to
• Add Making-A-Pull-Request how-to
• Add Reviewing-A-Pull-Request how-to
• Add Triaging-An-Issue how-to
• Link all new guides in Contributing.rst toctree
• Update Contact.rst to link new guides
• Update index.rst to mention community guides
• Add quick start section to Contributing-To-ROS-2-Documentation.rst
• Add language summary table to Code-Style-Language-Versions.rst

Did you use Generative AI?

Gemini used to help write the new RST files with better wording.

Additional Information

No new dependencies. Build passes with no warnings or errors.

[fujitatomoya]

i'm not against adding contribution guides in principle, but this is fairly standard Git/GitHub workflow that's already well documented elsewhere. i'd rather not maintain generic workflow docs in this repo unless they capture procedures or rules specific to ROS 2 contributions. let's hear more feedback on this.

[Supull]

i'm not against adding contribution guides in principle, but this is fairly standard Git/GitHub workflow that's already well documented elsewhere. i'd rather not maintain generic workflow docs in this repo unless they capture procedures or rules specific to ROS 2 contributions. let's hear more feedback on this.

Thanks for the feedback I will keep an eye on the discussion