Expose Cloud SDK on PATH via containerEnv, drop gcloud symlink

[shokkunrf]

Summary

• Expose the whole Cloud SDK on PATH via containerEnv (/usr/local/google-cloud-sdk/bin:${PATH}) instead of symlinking only gcloud into /usr/local/bin — this also puts gsutil, bq, and the rest of the bundled commands on PATH
• Drop the gcloud-only symlink from install.sh: a feature's containerEnv is emitted as a real ENV layer in the built image, so PATH is inherited by docker run, by images that FROM this one, and by later features in the same build — making the symlink redundant
• Bump the feature version to 1.0.2