Add OTLP authentication section to ./java/sdk.md

[jack-berg]

In opentelemetry-java, we receive recurring questions about how to accommodate various authentication requirements with OTLP exporters. This PR adds a new "Appendix -> OTLP exporters -> Authentication" section, including a code snippet demonstrating how programmatic config can be used to provide a dynamic authentication credential, such as a JWT.

Depends on first merging open-telemetry/opentelemetry-java-examples#565 and updating this PR with the updated opentelemetry-java-examples hash.

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Preview: https://deploy-preview-5866--opentelemetry.netlify.app/docs/languages/java/sdk/

[chalin]

Quick question: is the update of content-modules/opentelemetry-java-examples intentional, and essential in the scope of this doc addition?

As you can see from https://github.com/open-telemetry/opentelemetry.io/actions/runs/12588143748/job/35085436884?pr=5866, the check is failing because the submodule isn't pinned right (or it is pinned right and the submodule update needs to be rolled back).

(Oops, I just read the rest of your opening comment and see that the submodule update is likely intentional, and pending committed changes to that repo. Once the repo is updated, this PR will need to update the submodule PIN ID.)

[chalin]

See inline for comments on the prose.

[jack-berg]

Thanks @chalin!

[chalin]

LGTM.

Are we waiting for any other java-*-approvers?

[jack-berg]

Are we waiting for any other java-*-approvers?

I don't think we need to since this is low stakes. If any have recommendations for changes, we can make them in a followup.