Number of Attempts on SCM Material failure

**Some Context**
We use github as our SCM. We have several jobs that run nightly - either running tests or doing some data processing. Once in a while, github or our network has connectivity issues and the git clone/update fails. We get notified via emails of such a failure. If someone notices it and retriggers, things work fine and the jobs complete on time by morning. In case, some one does not notice, we will have to restart the pipeline in the morning and our jobs get delayed by few hours. 

**Changes in this PR**
- Number of Attempts for retrying materials upon failure. Default behaviour is 1. 
- Retry Interval in seconds before re-trying again. Default is 10. 

What are these getters and setters needed for, here? I understand the need for the ones in ScmMaterialConfig.