Do not restrict number of Q2T servers

The number of Q2T (Quorum-to-Tessera) servers is currently restricted to needing at least 1.

If we allowed no Q2T servers, then a Tessera node could act as a bootnode (a publicly known known node that all members could list in their initial peers, in order to bootstrap into the network), or as an archival node using the alwaysSendTo configuration parameters of a “sister node”.

[chris-j-h]

Perhaps keep the flag general and explicit - allowNoQ2T or disableQuorumCommunication, something along those lines.

[melowe]

Loosening validation will result in more user queries and documentation. Using a config option to enable boot node mode is fine (we are not functionally disabling anything, the user is enabling).

1. Bootnode mode could be defined implicitly (if no q2t defined) and then warn the user that its starting in this mode. In this case we take away validation.
2. An exploit bootnode config will allow us to fork the validation according to run mode. This will allow us to validate and feedback to the user the error of his/her/their ways.

I would suggest option 2. Option 1 might seem quicker but gains will be lost with support questions and documentation.