move cmd/pdatagen -> model/internal/cmd/pdatagen

[codeboten]

Description:
moving cmd/pdatagen code to model/internal

Link to tracking Issue: Fixes #4241

This is just the move of the package over, I can move model/internal/pdatagen/internal next, but wanted to minimize the changes in this PR.

[codecov]

Codecov Report

Merging #4243 (cb33572) into main (b927925) will increase coverage by 0.14%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #4243      +/-   ##
==========================================
+ Coverage   87.92%   88.07%   +0.14%     
==========================================
  Files         173      173              
  Lines       10263    10188      -75     
==========================================
- Hits         9024     8973      -51     
+ Misses        993      975      -18     
+ Partials      246      240       -6     

Impacted Files	Coverage Δ
model/pdata/generated_common.go	100.00% <ø> (ø)
model/pdata/generated_log.go	96.53% <ø> (ø)
model/pdata/generated_metrics.go	96.63% <ø> (ø)
model/pdata/generated_resource.go	100.00% <ø> (ø)
model/pdata/generated_trace.go	96.76% <ø> (ø)
config/identifiable.go	100.00% <0.00%> (ø)
config/configauth/configauth.go	85.71% <0.00%> (+3.89%)	⬆️
config/configunmarshaler/defaultunmarshaler.go	100.00% <0.00%> (+4.45%)	⬆️
config/configmap.go	81.98% <0.00%> (+10.24%)	⬆️

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[bogdandrutu]

Keep model/internal/cmd