Improve support for publishing build artefacts

[JamesDawson]

Currently the run-scripted-build composite action has inputs that allow the caller to specify files that should be published as build artefacts. However, this means those files must be known ahead of time and are effectively hard-coded in the workflow. It would be preferable to support something more akin to the ##vso[artifact.upload ...] functionality available in Azure DevOps.

NOTE: As background, the current limited solution was added to solve a particular problem, whereby a deployment job in the same workflow needed to know the container image tag that had been used by the build job. The tag is derived by the build via GitVersion, but we didn't want the deployment job to have a dependency on having access to the git repo, which would have allowed it recalculate the same version tag.

This issue suggests a solution that turns the design the around in order to make it more flexible.

1. Scripted build framework updated to emit 2 additional outputs: artefactName & artefactPath
2. Existing actions/upload-artifact step driven by the above step outputs (rather than the current composite action inputs)
3. Consider updating build framework with explicit artefact collation functionality, given that we still won't be able to specify arbitrary artefacts, since the actions/upload-artifact action requires one of a file, directory or wildcard pattern.

TODO:

• Decide whether to deprecate the existing composite action inputs (i.e. artefactName & artefactPath) or whether to enable the build framework to optionally consume them