Add support for multiple compute clusters during combined benchmarks (CH_Benchmark)

[sfc-gh-mjohansson]

Hi, today many vendors support the use of multiple compute clusters sharing the same data (Snowflake, Firebolt, Singlestore etc). For combined benchmarks with multiple such as CH_Benchmark it would be great if we can configure the <connection per instead of a single global .

For example: jdbc:postgresql://db.xyz.com/..." -- here goes the rest of the connection params ---

[bpkroth]

This would also be useful for testing traditional replicated cluster setups where read-only transactions can be directed at an alternative location either by hostname or through connection properties: https://learn.microsoft.com/en-us/azure/azure-sql/database/read-scale-out?view=azuresql