No validation of size or format on CLI parameters for the validator metadata

[phy-chain]

CLI endpoint change-metadata does not seem to enforce any format or size limit for the fields email and discord handle.
Given that these fields are displayed in a lot of webapps, it could break their UI or lead to security issues maybe.

Discord actually has some rules on what's allowed in that field. Same for emails, their is a RFC for that.

Transaction is accepted :

So far, from what I've seen change-metadata and initValidator are concerned.

PR with fix suggestion is coming...

[brentstone]

@phy-chain feel free to leave any comments on #2845. Figure we don't need anything complicated, can restrict it quite a bit, and character length is sufficient vs data size.