Update horizon v2.11.0 changelog (stellar#4072)

services/horizon: Register new ingestion metrics (stellar#4026)

Register new metrics introduced in bbccb6a and 68b39bd. Metrics that are not
registered are not available to metrics collector.

services/horizon: Final 2.9.0 fixes (stellar#4002)

This PR fixes final bugs found in Horizon 2.9.0RC:
* Correctly set `offer_id` in `/trades` when both: base and counter offers have
IDs assigned by Stellar-Core.
* Activate breaking change in `/trade_aggegations` on protocol upgrade (similar
to c858d7c).
* Fix paths starting with multiple slashes in `horizon-cmp`.
* Bumped Stellar-Core to 18.0.3.

protocol/horizon/operations: fix AllowTrust comment to use SetTrustLi…

…neFlags stellar#3998

What
This PR fixes the deprecation comment for AllowTrust so that users can be directed to the right operation.

Why
TrustlineFlagsUpdated is an effect, not an operation.

Known limitations
N/A

txnbuild, clients/horizonclient: Release v8.0.0-beta.0. (stellar#3981)

services/horizon: Horizon 2.9.0 CHANGELOG (stellar#3978)

Horizon 2.8.3 CHANGELOG (stellar#3950)

services/horizon: Horizon 2.8.2 CHANGELOG (stellar#3920)

services/horizon: Update changelog for v2.8.1 release (stellar#3851)

* Update changelog for v2.8.1 release

* fix state rebuild version

Update changelog for horizon 2.8.0 release (stellar#3830)