add changelog

.changelog/2525.breaking.md

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+go: Rename compute -> executor.
+
+It was proposed that we rename the "compute" phase (of the txnscheduler, _compute_, merge workflow) to "executor."
+
+Things that remain as "compute":
+- the registry node role
+- the registry runtime kind
+- the staking threshold kind
+- things actually referring to processing inputs to outputs
+- one of the drbg contexts
+
+So among things that are renamed are fields of the on-chain state and command line flags.