TEL-892: Overriding the To user when req.ToUserOverride is present

[genseric-ghiro]

Summary

• Follow up to TEL-892 Adding to_user_override field protocol#1717
• Overriding the To user when req.ToUserOverride is present
• Bumped the protocol version to point at the new overrideToUser field

[nishadmusthafa]

Yeah, if there's no way to bypass the protocol validation, I think we should be good.

[genseric-ghiro]

Yeah, if there's no way to bypass the protocol validation, I think we should be good.

The format validation for userToOverride is already done in NewCreateSIPParticipantRequestResult at the protocol level. However, CreateSIPParticipantRequest is an exported field, so it could be set directly without using the constructor (which isn't the case anywhere today). To prevent that edge case, adding some validation at the sip level as well.