Add test runner for new BLS tests

[michaelsproul]

Description

There is a new suite of tests for BLS here: https://github.com/ethereum/bls12-381-tests/

Looking at the test format, it's very similar to the existing tests, so we should be able to re-use much of the code in testing/ef_tests/src/cases/bls_*.

[zsluedem]

@michaelsproul Hello. I am looking around and trying to take this one. But I am not sure if this issue is obsolete or not.

Currently, the BLS_tests are using the test cases provided in https://github.com/ethereum/consensus-spec-tests. But the latest version 1.2.0-rc.1 of consensus-spec-tests already excluded these bls test cases generated by https://github.com/ethereum/bls12-381-tests/ and only keeps the eth related ones.

So the question is -> how would you like this new suite of tests for BLS to be downloaded? Should I add a new download process from https://github.com/ethereum/bls12-381-tests/releases/tag/v0.1.1 ?

[michaelsproul]

Resolved by #3235!