Added Whats New for engine 3.8 [skip CI]
Added Whats New for engine 3.8 [skip CI]


Former-commit-id: eb2a9e28449367b49f5e58df7062e2b785139962 [formerly 0d61706d85bf29a207f34732d91a8a3a7b3db0e9]
Former-commit-id: 38c87fc528d64adcfee734c4aaf4c885add39e77
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine