Set runtime security custom policy using config map

[lebauce]

Allow either adding a custom policy for runtime security or overriding the default one through a configmap.
Motivation

The default policy is part of the base image but was overridden by the configmap. Every time we bumped the
default policy we had to also bump the configmap. As the policy is tied to the runtime security agent, it
introduced hard to address compatibilities issues.

Additional Notes

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[codecov-commenter]

Codecov Report

Merging #315 (6e82292) into main (8b4b796) will decrease coverage by 0.15%.
The diff coverage is 55.31%.

@@            Coverage Diff             @@
##             main     #315      +/-   ##
==========================================
- Coverage   58.22%   58.06%   -0.16%     
==========================================
  Files          59       59              
  Lines        6300     6312      +12     
==========================================
- Hits         3668     3665       -3     
- Misses       2362     2376      +14     
- Partials      270      271       +1     

Flag	Coverage Δ
unittests	58.06% <55.31%> (-0.16%)	⬇️

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

Impacted Files	Coverage Δ
controllers/datadogagent/utils.go	81.11% <54.34%> (-0.96%)	⬇️
controllers/datadogagent/systemprobe.go	96.42% <100.00%> (ø)

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