Exclude git metadata from deployment images

[sylvesterkaczmarek]

Summary

• Add .git to the Deployment Manager's generated .dockerignore.
• Keep all existing generated ignore entries and Dockerfile behavior unchanged.

Motivation

The generated Dockerfile uses COPY . ., while the generated .dockerignore currently excludes virtual environments, .env, data, uploads, and other local state but not the project's .git directory.

For a Git-backed project, that sends repository history and metadata into the Docker build context and can copy it into the image. Besides unnecessary build context and image size, this can expose commit history, branch metadata, and configured repository remotes inside the built container.

The generated ignore file should exclude .git by default. Existing user-supplied .dockerignore files are not overwritten by this helper.

Validation

This is a single added ignore entry:

• generated .dockerignore now excludes .git
• application source files remain included
• existing ignore entries are unchanged
• existing project .dockerignore files remain untouched

Self-review

• One-line correctness/hardening change in one file.
• Dockerfile commands and deployment behavior are otherwise unchanged.
• No dependencies, notebooks, registry entries, or documentation changed.
• Searched open PRs for an existing Deployment Manager .git ignore fix and found none.

Maintainers may modify the branch if needed.