[mdatagen] Add semconv reference for attributes in metadata schema

[osullivandonal]

Description

This PR adds support in mdatagen for defining semantic conventions references for attributes.

Updating your attribute in metadata.yaml:

attributes:
  state:
    description: Breakdown of memory usage by type.
    type: string
    enum: [buffered, cached, inactive, free, slab_reclaimable, slab_unreclaimable, used]
    semantic_convention:
      ref: system.md#system-memory-state

Important

This work also updates the semantic_convention: ref: to use a relative URL, this was done as we want to ensure the same semconv version from the metadata schema is used, otherwise the end user could have a full url in ref with one semconv version and the schema version being a different version. A new method has been introduced in mdatagen that builds the semconv url at runtime.

Creates this table in the generated docs for that component:

Attributes

Name	Description	Values	Requirement Level	Semantic Convention
state	Breakdown of memory usage by type.	Str: buffered, cached, inactive, free, slab_reclaimable, slab_unreclaimable, used	Recommended	state

Link to tracking issue

This work is linked to #13297 but doesn't close it.

Testing

• loader_test.go was updated with attributes for cpu and state.
• Also cmd/mdatagen/internal/samplereciever was updated and generate code created which creates tests.

Documentation

The documentation template has been updated to reference the semconv definition for attributes if provided in the schema.

[codecov]

Codecov Report

❌ Patch coverage is 65.89595% with 59 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.22%. Comparing base (01ca829) to head (0652f5b).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
...plereceiver/internal/metadata/generated_metrics.go	69.15%	31 Missing and 2 partials ⚠️
...mplereceiver/internal/metadata/generated_config.go	31.57%	24 Missing and 2 partials ⚠️

❌ Your patch status has failed because the patch coverage (65.89%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14646      +/-   ##
==========================================
- Coverage   91.32%   91.22%   -0.11%     
==========================================
  Files         697      697              
  Lines       44456    44624     +168     
==========================================
+ Hits        40601    40707     +106     
- Misses       2716     2773      +57     
- Partials     1139     1144       +5     

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[ChrsMark]

I think that addition will be helpful at the moment to link existing attributes to defined Semantic Conventions.

I would like to use this already in https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/processor/k8sattributesprocessor/documentation.md as part of open-telemetry/opentelemetry-collector-contrib#44483.

@mx-psi @dmitryax please take a look

[mx-psi]

LGTM, ready to merge once the CI is fixed