scripts: Add script to convert resultstore schemas

This script is standalone and takes a CSV resultstore in the v1 schema
format as input and outputs a CSV resultstore in the v2 schema. v2 adds
support for multi-node SUTs and multi-role benchmarks.

In the v1 schema, each SUT implicitly has a single node and each
benchmark implicitly has a single role ("executer"). This also means
there is a single implicit mapping from each benchmark/role to the
single node of the sut upon which the benchmark is running.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>