Update init command to use DownloadConfigType

[tayfunelmas]

To be coordinated with the next Nearcore release.

In #12072 we change the --download-config parameter to take a string specifying the type of the node in order to download configuration for the specific type.

Update the lake indexer code and documentation to reflect this change. Note that we need to coordinate this with the next release of nearcore (see the TODO in the Cargo file).

Tracking issue: https://github.com/near/nearcore/issues/12070