fix: get volume size recommendations when in shadowfork mode (#820)
config:
```yaml
network_params:
network: "holesky-shadowfork"
persistent: true
```
fixes
```
There was an error interpreting Starlark code
Evaluation error: key "holesky-shadowfork" not in dict
at [github.com/ethpandaops/ethereum-package/main.star:143:55]: run
at [github.com/ethpandaops/ethereum-package/src/participant_network.star:134:48]: launch_participant_network
at [github.com/ethpandaops/ethereum-package/src/el/el_launcher.star:130:35]: launch
at [github.com/ethpandaops/ethereum-package/src/el/geth/geth_launcher.star:59:24]: launch
at [github.com/ethpandaops/ethereum-package/src/el/geth/geth_launcher.star:298:39]: get_config
Error encountered running Starlark code.
```
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