Obtain record cleaner rules

[JimBacon]

The record cleaner service will need to

• access and possibly copy the record cleaner rules that will be stored in https://github.com/BiologicalRecordsCentre/record-cleaner-rules
• automatically take account of any updates made to the rules

[JimBacon]

It uses Git pull to obtain a copy of the rules and manage updates. Updating of rules is triggered by an administrator calling the /rules/update endpoint.