Set build description, disable concurrent builds and build discarder using declarative pipeline in Jenkins

When you are writing declarative pipeline sometime you want to write code for to disable concurrent builds, build discarder and you also want to set some build description for multi-branch pipeline job.

following code can help you to implement these functionality.  

Reference:  

https://support.cloudbees.com/hc/en-us/articles/115000237071-How-do-I-set-discard-old-builds-for-a-Multi-Branch-Pipeline-Job