Kowalski filters: support new keywords

[Theodlz]

Add support for:

• autosave.saver_id, allowing Kowalski to use a different user account to autosave candidates as sources to a group, useful to not have everything posted by the kowalski-bot account both for book-keeping and to allow TNS autoreports from properly configured bot accounts.
• auto_followup.priority_order, so Kowalski knows if the instrument API associated to the allocation selected has descending or ascending priority values.
• auto_followup.implements_update, so Kowalski knows if the priority of an existing request can be updated or not.

[mcoughlin]

LGTM