BaseTransactionProcessor cannot process multiple threads with multiple similar transaction bundles

[TipzCM]

BaseTransactionProcessor cannot process multiple similar transaction bundles at the same time.

If 2 (transaction) bundles are submitted with similar resources within them (with unique fields), race conditions exist that will fail if both are processed simultaneously.

[TipzCM]

https://github.com/hapifhir/hapi-fhir/pull/4739/files