Horizon 1.5.0 support

[abuiles]

Horizon 1.5.0 added a new field to the ledgers resource called tx_set_operation_count, if your SDK has support for /ledgers or ledger resources, then it should include this new field. The value can be a number or null.

This value represents the total number of operations in the transactions set. You can use it to find out if recent ledgers have been full (and therefore subject to surge pricing) or not.

Are you curious about other changes in Horizon?

My two picks are:

1. The removal of --ingest-failed-transactions flag, which means from now on Horizon will always ingest failed transactions. If you run your own Horizon, this might have an impact on your database.
2. A new experimental mode of doing database reingestion which uses a Stellar Core subprocess instead of a persistent Stellar Core database. Please give this a try and let us know if you find any issue!

You can see the full changelog in the release notes https://github.com/stellar/go/releases/tag/horizon-v1.5.0