Validator Keys / Tokens in separate file

[carlhua]

Summary

Currently, configuring a server to validate involves creating either a [validator_seed] entry or a [validator_token] entry.

This is a problem because those entries contain the information necessary to validate and can be accidentally leaked when a validator operator is asking for assistance and is instructed to show parts of their configuration.

We should store the necessary data (seed or token) in a separate file that is either referenced by name in the main config or specified by a command line option.

For example:
[validator]
credentials=/path/to/whatever

Or:

/opt/ripple/bin/rippled --validator-credentials=/path/to/whatever

Exported from RIPD-1716

[carlhua]

Scott Determan wrote:

How about adding a general purpose way to include other files in our config file? Syntax TBD, but as a placeholder I like
@path/to/file

That syntax is from a thread about adding includes to toml here: toml-lang/toml#81