otelconf: add unmarshaling and validation for span & cardinality limits

[codeboten]

Adds unmarshaler code for SpanLimits and CardinalityLimits which require validation to ensure fields are set following the boundaries set by the schema.

Part of breaking up #8026

[codecov]

Codecov Report

❌ Patch coverage is 94.93671% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.7%. Comparing base (bbc51b2) to head (fee3bbb).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
otelconf/config_common.go	90.6%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #8043     +/-   ##
=======================================
+ Coverage   79.6%   79.7%   +0.1%     
=======================================
  Files        187     190      +3     
  Lines      11833   11912     +79     
=======================================
+ Hits        9420    9495     +75     
- Misses      2059    2062      +3     
- Partials     354     355      +1     

Files with missing lines	Coverage Δ
otelconf/config_json.go	100.0% <100.0%> (ø)
otelconf/config_yaml.go	100.0% <100.0%> (ø)
otelconf/config_common.go	90.6% <90.6%> (ø)

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[dmathieu]

This looks good. But it seems it should have a changelog entry.

[codeboten]

This looks good. But it seems it should have a changelog entry.

changelog added

[codeboten]

/easycla