Add BUILD_OS to Telemetry

[AlexFenlon]

Proposed changes

This collects the base Build_OS whenever an image is build and adds it to telemetry as shown below.

snippet of the log for when debian image with nginx plus is deployed:
BuildOS:debian-plus}}

snippet of the log for when alpine image with nginx oss is deployed:
BuildOS:alpine}}

snippet of the log for when debian image with nginx oss is deployed:
BuildOS:debian}}

Resolves: #5954

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[ADubhlaoich]

LGTM, though I am not approving since this is primarily a code PR.