Improve telemetry event for OS info

[pgombar]

Description

Make telemetry event introduced in PR #1635 a permanent one and move the event creation later, after monitoring handler has been instantiated, since otherwise the ContainerId might not be initialized when sending the event.

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PR information

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This change is 

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (develop@b82a31b). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff             @@
##             develop    #1698   +/-   ##
==========================================
  Coverage           ?   67.62%           
==========================================
  Files              ?       80           
  Lines              ?    11481           
  Branches           ?     1608           
==========================================
  Hits               ?     7764           
  Misses             ?     3375           
  Partials           ?      342

Impacted Files	Coverage Δ
azurelinuxagent/ga/update.py	88.42% <100%> (ø)
azurelinuxagent/common/event.py	83.76% <100%> (ø)

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[larohra]

LGTM