Add vendor_version for build info

[shamsher31]

To fix istio/istio#33421

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[istio-testing]

Skipping CI for Draft Pull Request.
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[howardjohn]

IMO "vendor version" should not be a concept. For example:

"serverVersion": {
    "major": "1",
    "minor": "20+",
    "gitVersion": "v1.20.6-gke.1400",
    "gitCommit": "b7ccf3218bdb80cd2d66ed6186d78f18f1ef03c6",
    "gitTreeState": "clean",
    "buildDate": "2021-05-05T09:19:45Z",
    "goVersion": "go1.15.10b5",
    "compiler": "gc",
    "platform": "linux/amd64"
  }

GKE k8s version. The "vendor" aspect is just in the normal version

[mandarjog]

@shamsher31 in the build if VERSION is set it is used to link stamp binaries. We will now set that VERsIOn to the full version including Google specific extensions. Like 1.10.2-asm.5

[istio-testing]

@shamsher31: PR needs rebase.

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