Adding first campaign: XIAO Showdown

[silabs-akosj]

Description

Adding a new folder for the first campaign.

Related Issue

NA

Changes Made

Adding readme about the XIAO Showdown campaign
Adding related reviewers in CODEOWNERS

Checklist

• I have read the Contributor License Agreement.
• I have followed the repository's coding guidelines .
• I have checked the action workflow results and they are all passed.

Additional Notes

[AndrasZiegler]

This pull request introduces a new developer competition campaign and updates several configuration and workflow files to support the campaign and improve code convention enforcement. The most significant changes are the addition of the XIAO Showdown 2025 campaign materials, updates to code ownership and formatting tools, and workflow improvements for pre-commit configuration.

Campaign Addition:

• Added the full campaign page for the XIAO Showdown 2025 developer competition, including contest details, prizes, entry instructions, judging rubric, resources, key dates, and terms and conditions in campaigns/XIAO-Showdown-2025/XIAO-Showdown-2025.md.

Repository and Workflow Configuration:

• Updated .github/CODEOWNERS to assign ownership of the new campaign folder to the community creations campaigns reviewers team.
• Updated the submodule reference for .github/coding-convention-tool to a newer commit, potentially bringing in fixes or features for code convention enforcement.
• Enhanced the workflow in .github/workflows/00-Check-Code-Convention.yml to apply a custom formatting configuration and dynamically update pre-commit exclusion patterns for specific files, improving automation and consistency.

Formatting and Spellcheck:

• Added "THT" to the ignore list in .github/formatting_config/ignore-words.txt to prevent false positives during spellchecking, likely due to its relevance in hardware/PCB context.