[Backport v1.27] Restore system-probe DSD socket volumeMount

[dd-octo-sts]

Backport a580b06 from #3001.

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What does this PR do?

See title

Motivation

system-probe needs DSD socket to write metrics to it (was removed in #2985) when direct mode is enabled (no security-agent)

Additional Notes

Anything else we should know when reviewing?

Minimum Agent Versions

Are there minimum versions of the Datadog Agent and/or Cluster Agent required?

• Agent: vX.Y.Z
• Cluster Agent: vX.Y.Z

Describe your test plan

Staging

Checklist

• PR has at least one valid label: bug, enhancement, refactoring, documentation, tooling, and/or dependencies
• PR has a milestone or the qa/skip-qa label
• All commits are signed (see: signing commits)

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 40.76%. Comparing base (a97d1de) to head (a9494f1).

Files with missing lines	Patch %	Lines
...controller/datadogagent/component/agent/default.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            v1.27    #3006      +/-   ##
==========================================
- Coverage   40.76%   40.76%   -0.01%     
==========================================
  Files         332      332              
  Lines       28198    28199       +1     
==========================================
  Hits        11495    11495              
- Misses      15928    15929       +1     
  Partials      775      775              

Flag	Coverage Δ
unittests	40.76% <0.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...controller/datadogagent/component/agent/default.go	44.23% <0.00%> (-0.07%)	⬇️

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