Upgrade Guide Should Note Change in Span Metrics

[Version v0.0.177](https://github.com/coralogix/telemetry-shippers/blob/master/otel-integration/CHANGELOG.md#v00177--2025-05-22) changed Span Metrics to be enabled by default. I think this should be mentioned in the UPGRADING guide since it has the potential for drastically increased metric production in cases in which span names have a high cardinality.