Update Docker integration guide to prefer COPY over ADD for simple cases (#16883)

## Summary

Docker best practices recommend to use `COPY` when the additional
functionality of `ADD` is not used.

See:
- https://docs.docker.com/build/building/best-practices/#add-or-copy
-
https://www.docker.com/blog/docker-best-practices-understanding-the-differences-between-add-and-copy-instructions-in-dockerfiles/

## Test Plan

Docs only change

docs/guides/integration/docker.md

@@ -163,7 +163,7 @@ If you're using uv to manage your project, you can copy it into the image and in
 
 ```dockerfile title="Dockerfile"
 # Copy the project into the image
-ADD . /app
+COPY . /app
 
 # Sync the project into a new environment, asserting the lockfile is up to date
 WORKDIR /app
@@ -412,7 +412,7 @@ RUN --mount=type=cache,target=/root/.cache/uv \
     uv sync --locked --no-install-project
 
 # Copy the project into the image
-ADD . /app
+COPY . /app
 
 # Sync the project
 RUN --mount=type=cache,target=/root/.cache/uv \
@@ -447,7 +447,7 @@ RUN --mount=type=cache,target=/root/.cache/uv \
     --mount=type=bind,source=pyproject.toml,target=pyproject.toml \
     uv sync --frozen --no-install-workspace
 
-ADD . /app
+COPY . /app
 
 RUN --mount=type=cache,target=/root/.cache/uv \
     uv sync --locked
@@ -487,7 +487,7 @@ RUN --mount=type=cache,target=/root/.cache/uv \
     uv sync --locked --no-install-project --no-editable
 
 # Copy the project into the intermediate image
-ADD . /app
+COPY . /app
 
 # Sync the project
 RUN --mount=type=cache,target=/root/.cache/uv \