[Collector Decentralization] Update bootstrapping Root Block command

[tim-barry]

Update the rootblock command that generates the consensus root block.

• New command-line flag: the RandomSource for the new epoch.
• New command-line flag: path to the previously-created clustering assignment
• New command-line flag: path to a directory with collector node votes
• Remove step: The rootblock command should no longer generate the clustering assignment, but instead read it from the new flag (as it is generated by a new boostrapping command).
• Add new step: the command should read the votes in the provided directory to generate the Cluster QCs for all cluster root blocks. This is similar to how the finalize command generates the Root QC for the root block.