feat: add cross reference pn_id in rdb instance

[yfodil]

Description of your changes

Fixes #

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 51 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@3e32178). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
apis/rdb/v1alpha1/zz_generated.resolvers.go	0.00%	35 Missing ⚠️
apis/rdb/v1alpha1/zz_generated.deepcopy.go	0.00%	16 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##             main     #81   +/-   ##
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  Coverage        ?   0.00%           
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  Files           ?     309           
  Lines           ?   30567           
  Branches        ?       0           
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  Hits            ?       0           
  Misses          ?   30567           
  Partials        ?       0           

Flag	Coverage Δ
unittests	0.00% <0.00%> (?)

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