Accept `prater` deposit files on the goerli launchpad

Deposit files made with older version of the staking-deposit-cli or with Wagyu Key Gen for the Goerli/Prater network are marked as made for `prater` in the deposit file. They should still be accepted on the Goerli launchpad (https://goerli.launchpad.ethereum.org/en/). They are currently rejected and they error out as being for the wrong network.

This is causing a lot of confusion and support for goerli validators.

Start at the Goerli launchpad's deposit-file network validation and trace the handling of files marked `prater`. Reproduce the rejection with an older staking-deposit-cli or Wagyu Key Gen file, then verify that valid Goerli/Prater files are accepted without weakening rejection of files for other networks.

Written by the indexing model from the issue text.