link-stamp binaries with vendor specific info

[mandarjog]

At present version.BuildInfo contains general istio info.

./out/linux_amd64/pilot-discovery version -o json

{
  "clientVersion": {
    "version": "1.11.6",
    "revision": "14db30df83cabb738ae9beb57d7219b3f273c3af-dirty",
    "golang_version": "go1.16.4",
    "status": "Clean",
    "tag": "1.7.0-alpha.0-3013-g14db30df83"
  }
}

We should add a vendor_version string for build info. This information is typically available in the docker build image, but that does not work for VMs.
For example at Google, the image names are pilot:1.9.5-asm.4 so 1.9.5-asm.4 is vendor version.

[mandarjog]

Alternatively vendors can just change the version link stamp to include 1.9.5-asm.4

[istio-policy-bot]

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