db-synthesizer does not use `ExperimentalHardForksEnabled` option

**Summary**

In [#4341](https://github.com/intersectmbo/cardano-node/pull/4341) `TestEnableDevelopmentHardForkEras` has been renamed to `ExperimentalHardForksEnabled` for `cardano-node`, but the configuration parser for `db-synthesizer` hasn't seen this change. As a result, calling `db-synthesizer` with a configuration file where the option is renamed results in behavior that is different from calling `cardano-node` with the same config. This unintuitive difference can lead to problems (see e.g. #1071) and time-consuming investigations.

**Completion criteria**
`db-synthesizer` displays the expected behavior when `ExperimentalHardForksEnabled` is enabled.

The ideal path to this solution is to separate out the parts of `cardano-node` and `ouroboros-consensus` that read node configuration in favor of a shared component. This will prevent any future divergence.

If investigation shows that such a separation would require an unreasonable restrucuring of the current code, it will suffice to update the parsers in `ouroboros-consensus` to match `cardano-node`.