Add Exasol benchmark support with TPC-H queries

[ooke]

This PR introduces Exasol support into the benchmark suite:

• Added run-exasol target in Makefile and integrated it into run-all.
• Introduced default SCALE_FACTOR variable for data generation.
• Implemented Exasol-specific runner (queries/exasol/) with schema creation, data loading, index enforcement, and statistics collection.
• Added all 22 TPC-H queries for Exasol.
• Added SQL scripts for schema creation, indices, and statistics.
• Updated README.md with Exasol configuration instructions and usage (make run-exasol).

This enables running the full TPC-H benchmark suite against an Exasol database.