[config] configopaque adoption

[mx-psi]

This is a meta issue for the implementation and adoption of the configopaque.String type alias on the configuration structs of Collector components.

This issue has the following items:

• Implement [proposal] Add string type alias for sensitive fields #5653
• Add security recommendation to use configopaque.String for sensitive fields. #6854
• Add examples and package documentation to the configopaque package. #6855
• [confighttp] Make Headers field opaque (fixed by [confighttp] Change Headers field type to have opaque values #6637)
• [configgrpc] Make Headers field opaque #6852
• [all][meta] Make existing sensitive configuration fields opaque opentelemetry-collector-contrib#17273