fix: Use ServiceName + MethodName as the regex for Otel

[lqiu96]

Fixes: https://github.com/googleapis/sdk-platform-java/issues/2502

Use a consistent Regex matching pattern for both gRPC and HttpJson. Copy the pattern used for gRPC into HttpJson.

Looking at the Method Descriptor for HttpJson (Compute as an example), the full method name does not match service.resource.action: https://github.com/googleapis/google-cloud-java/blob/1f9e63224424327a08e3663985773546b3f7808b/java-compute/google-cloud-compute/src/main/java/com/google/cloud/compute/v1/stub/HttpJsonBackendServicesStub.java#L85

It seems to match ServiceName/MethodName.

[sonarqubecloud[bot]]

Quality Gate failed for 'gapic-generator-java-root'

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Quality Gate failed for 'java_showcase_integration_tests'

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[sonarqubecloud[bot]]

Quality Gate failed for 'gapic-generator-java-root'

Failed conditions
1 Security Hotspot

See analysis details on SonarCloud

[sonarqubecloud[bot]]

Quality Gate failed for 'java_showcase_integration_tests'

Failed conditions
1 Security Hotspot

See analysis details on SonarCloud