Sharing pipeline yml files

At present the only way to specify a pipeline is to have a "bitbucket-pipelines.yml".

This causes a proliferation of files across all the projects. Nearly all the projects have similar pipelines with just the target name being changed. If we have to add a step or modify a step then we have to edit a lot of projects.

e.g.:

        - aws s3 mv serviceframework*.jar s3://<folder>/<app name>-test-$BUILD_VERSION-$BUILD_TIME.jar --metadata version="$BUILD_VERSION",time="$BUILD_TIME"

The app name and folder can also come as environment variables in the project.

What is needed is the ability to upload pipeline.yml files into the global settings for pipelines.
Then you should allow us to link the file to the project in the pipeline settings for the project. There will not be a bitbucket-pipelines.yml in the base folder of the project. It will only be a configuration setting in the bitbucket ui.

This is a very essential feature in order to avoid script file proliferation.