Support logs with no body

[codefromthecrypt]

Description

Right now, if you send a log event without a body, code will crash like below. This allows a log record body to be None, avoiding this error.

Overriding of current EventLoggerProvider is not allowed
Exception while exporting logs.
Traceback (most recent call last):
  File "/Users/adriancole/oss/otel-ollama/examples/python/opentelemetry/openai/.venv/lib/python3.12/site-packages/opentelemetry/sdk/_logs/_internal/export/__init__.py", line 307, in _export_batch
    self._exporter.export(self._log_records[:idx])  # type: ignore
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/adriancole/oss/otel-ollama/examples/python/opentelemetry/openai/.venv/lib/python3.12/site-packages/opentelemetry/exporter/otlp/proto/grpc/_log_exporter/__init__.py", line 111, in export
    return self._export(batch)
           ^^^^^^^^^^^^^^^^^^^
  File "/Users/adriancole/oss/otel-ollama/examples/python/opentelemetry/openai/.venv/lib/python3.12/site-packages/opentelemetry/exporter/otlp/proto/grpc/exporter.py", line 300, in _export
    request=self._translate_data(data),
            ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/adriancole/oss/otel-ollama/examples/python/opentelemetry/openai/.venv/lib/python3.12/site-packages/opentelemetry/exporter/otlp/proto/grpc/_log_exporter/__init__.py", line 108, in _translate_data
    return encode_logs(data)
           ^^^^^^^^^^^^^^^^^
  File "/Users/adriancole/oss/otel-ollama/examples/python/opentelemetry/openai/.venv/lib/python3.12/site-packages/opentelemetry/exporter/otlp/proto/common/_internal/_log_encoder/__init__.py", line 37, in encode_logs
    return ExportLogsServiceRequest(resource_logs=_encode_resource_logs(batch))
                                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/adriancole/oss/otel-ollama/examples/python/opentelemetry/openai/.venv/lib/python3.12/site-packages/opentelemetry/exporter/otlp/proto/common/_internal/_log_encoder/__init__.py", line 71, in _encode_resource_logs
    pb2_log = _encode_log(sdk_log)
              ^^^^^^^^^^^^^^^^^^^^
  File "/Users/adriancole/oss/otel-ollama/examples/python/opentelemetry/openai/.venv/lib/python3.12/site-packages/opentelemetry/exporter/otlp/proto/common/_internal/_log_encoder/__init__.py", line 57, in _encode_log
    body=_encode_value(log_data.log_record.body),
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/adriancole/oss/otel-ollama/examples/python/opentelemetry/openai/.venv/lib/python3.12/site-packages/opentelemetry/exporter/otlp/proto/common/_internal/__init__.py", line 90, in _encode_value
    raise Exception(f"Invalid type {type(value)} of value {value}")
Exception: Invalid type <class 'NoneType'> of value None

See discussion

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• [x] tox -e test-py312-opentelemetry-exporter-otlp-proto-common

Does This PR Require a Contrib Repo Change?

• [ ] Yes. - Link to PR:
• [x] No.

Checklist:

• [x] Followed the style guidelines of this project
• [x] Changelogs have been updated
• [x] Unit tests have been added
• [ ] Documentation has been updated