[ArPow] source-build job template should support custom buildScript parameters

[MichaelSimons]

Per feedback from @hoyosjs from the Diagnostics repo, the sourceBuild job template should support custom buildScript parameters. This is necessary for repos that need to specify custom parameters potentially along with a custom build script. It appears that you can use the buildscript parameter to include parameters e.g. buildscript: ./build.sh /p:myproperty=true but that is not intuitively obvious to the consumer.

[hoyosjs]

It's also not always supported for the parameter to be in the beginning in custom scripts. For example, properties need to be added at the end of the native build scripts in the runtime repo's scripts.

[MichaelSimons]

This is required to unblock ASP.NET CI. Turns out it isn't.