Fix CRI vs Docker socket path priority. Always try to mount default runtime dir if using standard path to maximize usage of Env AD

[vboulineau]

What does this PR do?

Currently, due to previous defaulting of DockerSocketPath, we're always mounting Docker set even if not existing.

Motivation

What inspired you to submit this pull request?

Additional Notes

Anything else we should know when reviewing?

Describe your test plan

On a containerd deployment, deploy Datadog Agent with both CriSocket.DockerSocketPath (to standard, non-existing, path) and CriSocket.CriSocketPath to containerd socket.
The resulting POD manifest should mount /var/run as runtimesocketdir and the containerd check should run properly.

[codecov-commenter]

Codecov Report

Merging #320 (164080a) into main (8072ba9) will increase coverage by 22.83%.
The diff coverage is 25.00%.

@@             Coverage Diff             @@
##             main     #320       +/-   ##
===========================================
+ Coverage   35.55%   58.39%   +22.83%     
===========================================
  Files          62       60        -2     
  Lines       10667     6362     -4305     
===========================================
- Hits         3793     3715       -78     
+ Misses       6592     2371     -4221     
+ Partials      282      276        -6     

Flag	Coverage Δ
unittests	58.39% <25.00%> (+22.83%)	⬆️

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

Impacted Files	Coverage Δ
controllers/datadogagent/utils.go	81.42% <25.00%> (-0.13%)	⬇️
api/v1alpha1/zz_generated.deepcopy.go
api/v1alpha1/zz_generated.openapi.go

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