Use volume mount in release build

[adambkaplan]

• Use bind mount instead of tar stream to add source code to the release
  container.
• Update release Dockerfile to declare volume for the s2i source.
  Command updated to remove tar stream in
• Add sti-version-defs file to .gitignore

[adambkaplan]

/assign @gabemontero

Seems that every time I try to release, I find something wrong with the s2i release script.
This go around, it seems that podman with cgroups v2 doesn't like the tar stream in. This seemed like a silly aspect of the release script anyway, since nowadays it's much easier to bind mount the source code into the container. Bind mounting also saves us the extra podman cp call - the resulting client binaries sit in the _output directory at the end of the build.

[gabemontero]

/lgtm

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