Honour previous parameter defaults between builds in Jenkinsfile

When the Jenkinsfile is being used in a job that was created by dsl and intended to be triggered by scm polling, e.g. post-commit, that dsl will want to set alternative defaults for the Jenkinsfile parameters.

By default each build of the Jenkinsfile will restore the job's default parameters (i.e. changing the defaults for the next build).

This is described in more detail here
https://www.linkedin.com/pulse/build-jenkins-job-default-parameters-using-bipin-kumar-chaurasia/ 

and summarised in a quick answer here
https://stackoverflow.com/questions/57745451/how-can-i-override-a-jenkinsfiles-default-parameters

Patch for this is here:
https://github.com/apache/cassandra/compare/trunk...thelastpickle:cassandra:mck/jenkinsfile-persist-parameters

I'm waiting on INFRA-25694 to see if there are any other problems/changes in the Jenkinsfile when it's running in ci-cassandra.a.o