Introduce Operation.asRepoInitString

for SLING-10219 (and maybe other use cases too) it would be great if org.apache.sling.repoinit.parser.operations.Operation would come with a asRepoInitString method that would allow to obtain the original repo-init statements.

I was checking if toString would allow to extract that (with a bit of extra effort) but unfortunately the default implementation is:

    public String toString() {
        return this.getClass().getSimpleName() + " " + this.getParametersDescription();
    }

and getParametersDescription isn't implemented in a consistent way and in some cases doesn't reveal all information needed.
further more even the toString method isn't consistent across the various operation implementations (e.g. RegisterPrivilege.toString actually coming close to the original statement and not including the simple class name)