Release a root and non-root Docker image switching to ENTRYPOINT

Changelog for 0.12.5:

• PR #813 Add root user to Dockerfile for Google Cloud Build by @utsavanand2
• PR #812 Ensure delete respects namespace value in stack file by @LucasRoesler
• PR #808 Override the stack.yaml namespace field from faas-cli. Fixes #742 by @utsavanand2
• PR #798 Move cli authentication to config package by @viveksyngh

Commits
372d120 Add root user for faas-cli invokation by @utsavanand2
9ac49b3 Ensure delete respects namespace value in stack file by @LucasRoesler
080cde3 Fixes #742 by @utsavanand2
1519c15 Return error from NewCLIAuth function by @viveksyngh
d4e8683 Return error from NewClient function by @viveksyngh
d2acc45 Move auth from config to proxy by @viveksyngh
2319347 Move cli authentication to config package by @viveksyngh

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