Add a changelog fragment for the tracing sublibrary

Author: jasagredo

changelog.d/20260908_120000_javier.sagredo_tracing_sublibrary.md

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+### Non-Breaking
+
+- Added a new public sublibrary `ouroboros-consensus:tracing`, holding the
+  `LogFormatting` and `MetaTrace` instances for Consensus types. These were in
+  `cardano-node`, and now live next to the types they describe, so that a change
+  to a traced type and the change to its rendering land in the same commit.
+
+  The sublibrary also exports `Ouroboros.Consensus.Tracing.HasIssuer`, the
+  `HasIssuer` class and its instances, and `Ouroboros.Consensus.Tracing.KESInfo`,
+  moved over from `cardano-node` for the same reason.