Add TurboCache to documentation of open source CAS/BRE services

[allada]

Adds TurboCache to the documentation for external/community projects that implement the BRE services.

[radvani13]

@allada hey can you please explain or provide more information. I am not familiar with turbo cache

[allada]

It's another BRE server similar to Buildbarn, Buildfarm, BuildGrid, Scoot. It provides serves both caching and remote execution.

Here's a few examples of cache configurations:
https://github.com/allada/turbo-cache/tree/master/config

Here's an example & documentation of a caching + remote execution terraform deployment for AWS:
https://github.com/allada/turbo-cache/tree/master/deployment-examples/terraform

There's a few big companies that use it in production.

ref: https://github.com/allada/turbo-cache