Remove ShardingSphere Agent support for Zipkin exporter

[linghengqian]

Feature Request

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Is your feature request related to a problem?

• See Bump the Otel SDK and Otel Semantic Conventions version #37717 .

Describe the feature you would like.

• The io.opentelemetry:opentelemetry-exporter-zipkin is deprecated and unmaintained. It doesn't even align with the dependencies of open-telemetry/opentelemetry-java, leading to the conclusion that everyone should only use OTLP. See Deprecate Zipkin exporter open-telemetry/opentelemetry-specification#4715 , https://opentelemetry.io/blog/2025/deprecating-zipkin-exporters/ and Deprecate zipkin exporter open-telemetry/opentelemetry-java#7863 .
• Incidentally, Zipkin also supports OTLP. See https://github.com/openzipkin-contrib/zipkin-otel/blob/main/module/README.md . Developers can continue to pass data to Zipkin via io.opentelemetry:opentelemetry-exporter-otlp.

At least for Java, the zipkin exporter uses dreprecated attributes and lacks resource attributes. If users want to send trace signals to Zipkin, they should use the otlp collector from zipkin-otel.

• I believe we should remove the use of io.opentelemetry:opentelemetry-exporter-zipkin. This includes removing all related documentation and unit tests, integration tests, and E2E tests.

[linghengqian]

As a first step in addressing this issue, it's clearly necessary to modify all the zipkin usage in the documentation for the zipkin outlet. I have a small test at linghengqian/shardingsphere-agent-master-test@b506e08 .

This requires adjusting the layout modified in #37751 . Of course, this change would be better placed in 5.5.4 or 6.0.0. Placing it on the 5.5.3 milestone seems a bit odd.