[mdatagen] Add support for example configurations in metadata.yaml

[sAchin-680]

Key Features:

• Optional example_configs field in metadata.yaml supporting multiple named examples
• Auto-generated documentation section showing example configurations
• Auto-generated validation tests ensuring examples are valid YAML
• Examples include name, description, and YAML configuration content

Changes:

• Add ExampleConfig struct and example_configs field to metadata schema
• Update documentation template to render example configurations section
• Generate TestExampleConfigs to validate example YAML syntax
• Fix unused import in config_test.go.tmpl (conditional confmap import)
• Add example configurations to samplereceiver and samplescraper as demos

Link to tracking issue

Addresses #14066 - Automate validation and fulfillment of criteria outlined in the "Component Stability" document
Fixes #14097 - Ensure all components have at least one sample configuration

Testing

• All existing tests pass (34 files updated, all tests green)
• New TestExampleConfigs validates each example configuration is valid YAML
• Documentation correctly renders example configurations with proper formatting
• Tested with multiple examples per component (samplereceiver: 3 examples, samplescraper: 1 example)

Documentation

• Updated metadata-schema.yaml with example_configs field documentation and usage examples
• Example configurations automatically render in generated documentation.md files
• Each example includes descriptive name and use-case description for clarity

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.21%. Comparing base (c503bb1) to head (d7a0f02).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14133      +/-   ##
==========================================
- Coverage   92.25%   92.21%   -0.04%     
==========================================
  Files         658      658              
  Lines       41168    41168              
==========================================
- Hits        37978    37963      -15     
- Misses       2183     2193      +10     
- Partials     1007     1012       +5     

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