Provide new "upgrade existing repo to ODS" quickstarter

Is your feature request related to a problem? Please describe.
Assuming you have your code somewhere version controlled, there is quite some manual steps one needs to do to get it into ODS. Namely:

1. pick any quickstarter in prov app (gets you jenkinsfile / sq and ocp resources)
2. clone / clean the created sources
3. add new remote and merge existing code

The reason why this is not (really) working today is 3 fold:

1. Provision app will fail if the repo already exists (https://github.com/opendevstack/ods-provisioning-app/blob/2b3773f77dcebed5b3388598020053365e67d5e7/src/main/java/org/opendevstack/provision/services/BitbucketAdapter.java#L587)
2. PushToRepo stage contains the upgrade magic in case the repo is already filled with state (https://github.com/opendevstack/ods-jenkins-shared-library/blob/master/src/org/ods/quickstarter/PushToRemoteStage.groovy)
3. CopyFilesStage (https://github.com/opendevstack/ods-jenkins-shared-library/blob/master/src/org/ods/quickstarter/CopyFilesStage.groovy#L13) - does a (blind) copy of quickstarter files, w/o checking if they already exist - so in case a jenkinsfile exists, it will fail ..

I want to solicit feedback on this first - to see what we could do ... my proposal would be to create

1. a new quickstarter (sort of based on the docker-plain) with checks on what's already in the repo - and adds jenkinsfile / sq props and also ocp resources .. .
2. add a check into the prov app if this new quickstarter is used, that the repo must already exist, and we only add roles / webhook proxy ...

@torstenhe @michaelsauter

Start by reading the referenced BitbucketAdapter.java location in ods-provisioning-app, then PushToRemoteStage.groovy and CopyFilesStage.groovy in ods-jenkins-shared-library. Compare their existing-repository behavior with the proposed docker-plain-based quickstarter and identify the expected provisioning and file-copy outcomes. Done requires an agreed design for the new quickstarter and Provision app behavior.