Is your feature request related to a problem? Please describe.
Currently, all OTEL sources (OTEL trace source, OTEL metric source and OTEL log source) does some transformations while creating events from OTEL data.

1. In all sources, the keys are created by replacing "." with "@" (dedotting)
2. In all sources, the attributes are "flattened" by moving them to the root of the event instead of nesting under "attributes"

The dedotting is done to make the data is compatible with OpenSearch.

Describe the solution you'd like
I think the transformations should be outside of the OTEL sources because sink is not always OpenSearch. Also, the users are not given any option to not do the transformations. We should remove the transformations from the OTEL sources and let users explicitly do this as a processor or OpenSearch sink option

   processor:
      - opensearch_compatibility_transform:
           flatten_attributes: true
           dedotting: true

or Alternatively

   sink:
     - opensearch:
           opensearch_compatibility_transformation: true

Describe alternatives you've considered (Optional)
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Additional context
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