opentelemetry-exporter-otlp-proto-http: fix certificate_file=False being ignored

[SFernandoS]

Description

The OTLPSpanExporter constructor used certificate_file or environ.get(...) to resolve
the certificate configuration. Because False is falsy in Python, passing
certificate_file=False explicitly (to disable SSL verification) was silently ignored,
falling back to the environment variable or the default True.

This PR changes the check to certificate_file if certificate_file is not None else environ.get(...)
so that only an unset parameter triggers the fallback.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Existing unit tests pass (tox -e py312-test-opentelemetry-exporter-otlp-proto-http)
• Manual verification that OTLPSpanExporter(certificate_file=False) now correctly
  stores False instead of falling through to the default

Does This PR Require a Contrib Repo Change?

• No.

Checklist:

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

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: SFernandoS / name: Fernando (57b8fbf)

[herin049]

It should be noted that the type signature for the constructor explicitly disallows passing in a bool

certificate_file: str | None = None,

That being said, I think it's ok to allow a bool to be passed here. Make sure to update the type signature.

[SFernandoS]

Good catch! I've updated the type signature to str | bool | None = None and pushed the change.

[SFernandoS]

Updated with the type signature fix as requested. Ready for another look.

[lzchen]

Any reason why we need to make this change? A bool is not a valid type so passing in False should be undocumented/unsupported behavior.

[herin049]

Any reason why we need to make this change? A bool is not a valid type so passing in False should be undocumented/unsupported behavior.

There is currently no way to disable TLS verification on the exporters. I suppose we could add another argument, but it's also pretty easy to support this way.

[SFernandoS]

The motivation is that there is currently no supported way to disable TLS verification for the OTLP HTTP exporter. I originally chose False because it required a minimal change while preserving backward compatibility.

That said, I agree overloading certificate_file with a boolean may not be the cleanest API. If the preferred direction is to introduce an explicit parameter (e.g. verify_ssl or insecure_skip_verify), I'm happy to rework the PR accordingly.

[SFernandoS]

I've opened #5416 as an alternative approach based on the API design discussion here. If maintainers prefer the explicit insecure parameter, I'm happy to continue with that proposal and close this PR.