Add enable_sensitive_methods to the witnet.toml

[Tommytrg]

In the Witnet configuration file, under the jsonrpc section, you can enable or disable sensitive methods, such as sendRequest or getPkh but the parameter name only appears in the code. To allow users to know about this option, we could add as default enable_sensitive_methods to true with a comment explaining it.

[jsonrpc]
enable_sensitive_methods = true