feat(docker): set default UV_TOOL_BIN_DIR on docker images (#13391)

Closes #13057

Sets `UV_TOOL_BIN_DIR` to `/usr/local/bin` for all derived images to
allow `uv tool install` to work out of the box.

Note, when the default image user is overwritten (e.g. `USER <UID>`) by
a less privileged one, an alternative writable location would now need
to be set by downstream consumers to prevent issues, hence I'm labeling
this as a breaking change for 0.8.x release.

Relates to https://github.com/astral-sh/uv-docker-example/pull/55

Each image was tested to work with uv tool with `UV_TOOL_BIN_DIR` set to
`/usr/local/bin` with the default root user and alternative non-root
users to confirm breaking nature of the change.

.github/workflows/build-docker.yml

@@ -225,6 +225,7 @@ jobs:
           cat <<EOF > Dockerfile
           FROM ${BASE_IMAGE}
           COPY --from=${{ env.UV_GHCR_IMAGE }}:latest /uv /uvx /usr/local/bin/
+          ENV UV_TOOL_BIN_DIR="/usr/local/bin"
           ENTRYPOINT []
           CMD ["/usr/local/bin/uv"]
           EOF