[AGE-2238] [Security] Update .env file handling to prevent security risks

[mmabrouk]

Background

Currently, the deployment guide instructs users to "Edit hosting/docker-compose/oss/.env.oss.gh." However, this file is not ignored by git, creating a security vulnerability where sensitive configuration values could be accidentally committed.

Impact

This creates a security risk for contributors and users who follow the documentation, potentially exposing sensitive configuration information if they commit changes to the repository.

Requirements

1. Rename the file to .env.oss.gh.default as a template

2. Update the documentation to instruct users to:

   • Copy the default file to .env.oss.gh
   • Make their changes in the copied file (which should be gitignored)

3. Ensure .env.oss.gh is properly added to .gitignore

Related Information

• Current documentation page: https://docs.agenta.ai/self-host/host-locally
• This issue was identified through user feedback from contributors trying to follow the deployment guide

_AGE-2238