Define interfaces for interacting with newly cleaned up import code

This is a bit of a placeholder but I think it will be necessary for integrations to

• add new user_job_types - currently this is a hard-coded list and the Parser class is hard-coded into it - we probably need to solve this to get the csvimporter working these are declared by any class that implements UserJobInterface
• alter the metadate - eg inject 'full_name' into the available fields to map to. UPDATE - am wondering if being able to add pseudofields for the api is enough - would work for full_name
• intervene once getMappedRow has run
• ideally we would extract out the lookup code where matching contacts are found or matching entities and add some interaction there - assuming the hook in findDuplicates is not enough. UPDATE - I think intervening at the end of getMappedRow will work
• be able to alter the validation of the mapping. I know a form rule could be added by hook but I think a specific hook is cleaner as the hook would also need to alter existing rules