[confmap] Add error hint when invalid YAML was passed

[mx-psi]

Description

Add error hint field to surface YAML parsing errors. This only surfaces the error for top-level URIs but it's a step in the right direction.

Link to tracking issue

Updates #12000

Testing

Documentation

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.76%. Comparing base (2447a81) to head (3ea155d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #12180   +/-   ##
=======================================
  Coverage   91.75%   91.76%           
=======================================
  Files         464      464           
  Lines       24763    24773   +10     
=======================================
+ Hits        22722    22732   +10     
  Misses       1656     1656           
  Partials      385      385           

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[mattsains]

One thing I noticed a lot while researching this issue is that a lot of the test cases only test that some kind of error was produced, and not the content of the error. Perhaps you could consider fixing that as part of this PR. Examples:

• https://github.com/open-telemetry/opentelemetry-collector/blob/main/otelcol/collector_test.go#L315C1-L316C1
• https://github.com/open-telemetry/opentelemetry-collector/blob/main/confmap/provider_test.go#L64
• https://github.com/open-telemetry/opentelemetry-collector/blob/main/confmap/provider_test.go#L80

Improving these tests would prevent a regression like this in the future, they're easy to find by searching for require.Error and easy to fix by changing them to require.EqualError(t, err, "expected message"). You can even just run the tests with the expected message set to blank and figure out what the expected error is.