opamp-client: add support for non-JSON effective configs

What problem do you want to solve?

The Python OpAMP client (opentelemetry-opamp-client) currently supports building effective config messages from JSON content. It would be useful to also support effective configs that have arbitrary MIME-types, represented as text or bytes.

This aligns with the OpAMP spec, which defines AgentConfigFile.body as raw bytes, and content_type as a MIME-type describing those bytes. My organization would like this capability to use the OpAMP client to emit the effective config as text/plain, newline-delimited, environment variables.

Describe the solution you'd like

I'd like to update the build_effective_config_message function to accept string or byte message bodies and arbitrary MIME types.

Describe alternatives you've considered

No response

Additional Context

No response

Would you like to implement a fix?

Yes

Tip

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