feat(fluid-build): Support additional executable names

[tylerbutler]

work in progress

The idea is to allow fluid-build to be exposed as a different executable name, so I can create an alternative CLI entrypoint.

After working on this, I now think it might be better to add custom task support to fluid-build so I could define my own task (it could even subclass the fluid-build task). But that itself is insufficient, because the "fluid-build" string is parsed in the core build graph creation process, so it's more core than the task layer. Another clue: the "fluid-build" string is not mapped to a task: https://github.com/microsoft/FluidFramework/blob/4c0c130f1df720694a1a1cab7fd0f22f792baac1/build-tools/packages/build-tools/src/fluidBuild/tasks/taskFactory.ts#L31-L72

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This PR has been automatically marked as stale because it has had no activity for 60 days. It will be closed if no further activity occurs within 8 days of this comment. Thank you for your contributions to Fluid Framework!