Add namespace labels to source metrics

[creydr]

Adding the namespace and source name tags to the metrics of the ApiServerSource and PingSource

[codecov]

Codecov Report

❌ Patch coverage is 68.96552% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.65%. Comparing base (223b43f) to head (73b7e01).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/observability/newcontext.go	0.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8892      +/-   ##
==========================================
+ Coverage   50.62%   50.65%   +0.02%     
==========================================
  Files         409      409              
  Lines       21657    21680      +23     
==========================================
+ Hits        10963    10981      +18     
- Misses       9839     9846       +7     
+ Partials      855      853       -2     

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[Cali0707]

/test reconciler-tests

[Cali0707]

/lgtm
/approve

Thanks @creydr !

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Cali0707, creydr

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