Refactor pipelines to use more source build infra from Arcade

Both SBE and SBRP having build pipelines which define custom jobs that directly call into the `/eng/common/templates/steps/source-build.yml` template. This requires [defining the container name](https://github.com/dotnet/source-build-reference-packages/blob/768378e775fc5ddc99d41f2c4d1c78182f326ea7/azure-pipelines/builds/ci.yml#L32) to be used. This means that has to be manually maintained rather than getting it for free from Arcade. We should investigate if it's possible to reuse more of the Arcade infra to avoid this. The use case is different here from product repos in that we _only_ want to execute source build legs. If nothing else perhaps we can use the [eng/common/templates/jobs/source-build.yml template](https://github.com/dotnet/arcade/blob/e91ff1729192ebae270f0d42502da51eeb853741/eng/common/templates/jobs/source-build.yml), if not one that's higher level than that.