Add changelog for 0.11.2 release (#1829)

CHANGELOG.md

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+# Changelog
+
+Due to the rapidly changing nature of ETH2 testnets and rapid rate of improvements to Teku, 
+we recommend most users use the latest `master` branch of Teku.
+
+## Upcoming Breaking Changes
+
+- In a future release the `--eth1-enabled` option will be removed. 
+  ETH1 will be enabled when an `--eth1-endpoint` is provided and otherwise disabled.
+
+## 0.11.2
+
+### Additions and Improvements
+
+- Updated to spec version v0.11.3.
+- Improved recovery from network changes. Peers are now disconnected if they do not respond for a 
+  period ensuring upstream network interruptions are detected and peers can reconnect.
+- The node's ENR is printed at startup even if the genesis state is not yet known.
+  As per the beacon chain spec, the network ports are still not opened until the genesis state is known.
+- OpenAPI schemas are now more compatible with code generating tools.
+- Include block root in `/beacon/block` responses.
+- Improved error messages when invalid or incompatible CLI options are provided.
+- Improved peer discovery by filtering out peers with incompatible `eth2` ENR fields.
+- Improved performance of BLS signature verification
+- Updated to jvm-libp2p 0.4.0
+
+### Bug Fixes
+
+- Fixed a deadlock condition which could cause block imports to silently stall.
+- Initial sync now reaches chain head correctly even when the chain has not finalized for more than 10 epochs.
+- Fixed `NullPointerException` and `ArrayIndexOutOfBoundException` intermittently encountered when importing blocks 
+  due to a concurrency issue in batch signature verification.
+- `/beacon/chainhead` reported incorrect slot and block root data.
+- Fixed a range of race conditions when loading chain data which could result in inconsistent views 
+  of the data or data not being found as it moved from recent to finalized storage.
+- Significantly reduced the number of ERROR level log messages. 
+  Invalid network data or unexpectedly disconnected peers is now logged at DEBUG level.
+- Storage system did not correctly prune blocks loaded from disk on startup when they became finalized.
+
+
+### Known Issues
+
+- This release provides support for the Witti testnet via `--network witti` however the configuration 
+  for this testnet is not yet stable and will likely differ from the one currently used.
+- The Schlesi testnet has been abandoned. The `--network schlesi` option will be removed in a future release.
+- Memory usage grows signficantly during periods of non-finalization.
+- Teku requires the ETH1 endpoint to keep historic world state available for at least the ETH1 voting period. 
+  This is typically more historic state than is kept when ETH1 nodes are pruning state. 
+  Workaround is to connect to an archive node or configure the node to preserve a greater period of historic world state.