Add `benchmark_mssql` make task and misc. improvements

[sassela]

Thanks so much for your help getting subscription benchmarks running on an MSSQL source this week. Here's my PR, as promised, with a few things that could make things easier for the next person (future me. I mean future me.) including:

• updates the graphql-engine version to support multiple sources
• a benchmark_mssql make task that sets up, runs and tears down example MSSQL benchmarks on the Chinook dataset
• a make task to set up the events table on a Postgres DB
• parameterise run-subscription-bench-docker.sh to accept a config file path
• make a few scripts executable (100644 → 100755) where it seems like they should be
• a make task and run docker stats tool cadvisor for subscriptions
  • I didn't spend too much time digging into why the json reports weren't supported, but followed your advice and went for the simplest web-based docker container stats tool.

This helped to smooth the workflow for my demo prep, but don't hesitate to ask me to revert things if they're not generally useful.

[GavinRay97]

Omg this is an amazing PR, thank you so much!