feature: modify anonymous end-to-end test

[lucasmenendez]

The goal of this issue is to update the current anonymous end-to-end test to include the new uses cases.

Until now, only users with account in the vochain (and a valid SIK) can cast anonymous votes. Now, a non registered user can cast a vote registering its SIK previously using the RegisterSIKTx proving that he or she is already included into the election census (census proof).

The new test version should include this use case, using 5 registered accounts to vote but also 5 new identities that are not registered in the vochain.

This issue requires the merge of #1080. In this PR, the e2e helpers had been modified to prevent the account creation if it is not desired. Also includes some new APIClient methods to register a temporal SIK.