Add gitGost topic for anonymous Git contributions

[livrasand]

Summary

This pull request adds a new topic, gitgost, to improve discoverability of tools and workflows related to anonymous Git contributions.

gitGost is a privacy-focused tool that enables developers to contribute to public repositories without exposing personal identity metadata such as name, email, or timestamps. Contributions are submitted through a neutral bot account and remain subject to standard maintainer review processes.

Why this is useful

Privacy in open source contributions is an increasingly relevant topic. Developers may wish to contribute without linking activity to their personal identity due to:

• Reducing exposure to scraping or unwanted data collection
• Avoiding permanent public contribution records for minor changes
• Contributing safely to sensitive or controversial projects
• Operating in environments with restrictive policies or risks

The gitgost topic helps group repositories and tools that explore this space, making them easier to discover and understand.

Changes included

• Added topics/gitgost/index.md with metadata and description
• Added a representative topic image (gitgost.png)

Notes

This contribution follows the repository guidelines:

• Uses neutral, informational language
• Avoids promotional tone
• Provides broadly useful context for the community

The goal is to improve topic curation around privacy and anonymous contribution workflows in Git.